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❓Kevin Kangaroo starts hopping on a number line at 0 and aims to reach 1. Now, he can hop only frac{1}{4} of the distance to the goal initially. However, due to the increasing difficulty, each subsequent hop can only cover frac{1}{4} of the remaining distance to the goal, and his efficiency to cover that fraction decreases by a factor of frac{3}{4} with each hop. How far has he hopped after six hops? Express your answer as a common fraction.
💡Okay, so Kevin the kangaroo is trying to hop from 0 to 1 on a number line. He starts by hopping 1/4 of the distance to the goal, which is 1. So, his first hop is 1/4. That makes sense because 1/4 of 1 is 0.25, right?Now, after the first hop, he's at 1/4. The remaining distance to the goal is 1 - 1/4 = 3/4. But here's the catch: each subsequent hop can only cover 1/4 of the remaining distance, and his efficiency decreases by a factor of 3/4 each time. Hmm, so not only is the remaining distance getting smaller, but his ability to cover that fraction is also decreasing. That sounds a bit tricky, but let's break it down step by step.Let me try to outline each hop:1. **First hop:** He hops 1/4 of the total distance, which is 1/4. So, total distance covered so far is 1/4.2. **Second hop:** Now, the remaining distance is 3/4. He can hop 1/4 of that, which is (1/4)*(3/4) = 3/16. So, after the second hop, he's covered an additional 3/16. Total distance now is 1/4 + 3/16.Wait, let me calculate that. 1/4 is 4/16, so 4/16 + 3/16 = 7/16. So, after two hops, he's at 7/16.3. **Third hop:** The remaining distance is 1 - 7/16 = 9/16. He can hop 1/4 of that, which is (1/4)*(9/16) = 9/64. But wait, the problem says his efficiency decreases by a factor of 3/4 each time. So, does that mean each hop is 3/4 of the previous hop's distance?Hold on, maybe I misunderstood. Let me read the problem again: "each subsequent hop can only cover 1/4 of the remaining distance to the goal, and his efficiency to cover that fraction decreases by a factor of 3/4 with each hop."So, it's two things: each hop is 1/4 of the remaining distance, and his efficiency (which I think refers to the fraction he can cover) decreases by 3/4 each time. Hmm, maybe I need to model this differently.Let me think. The first hop is 1/4 of the total distance. Then, each subsequent hop is 1/4 of the remaining distance, but each time, the fraction he can cover is multiplied by 3/4. So, the first hop is 1/4, the second hop is (1/4)*(3/4), the third hop is (1/4)*(3/4)^2, and so on.Wait, that might make more sense. So, each hop is 1/4 of the remaining distance, but the efficiency (the fraction he can cover) is decreasing by 3/4 each time. So, the first hop is 1/4, the second hop is (1/4)*(3/4), the third hop is (1/4)*(3/4)^2, etc.But then, the remaining distance after each hop would be the previous remaining distance minus the hop distance. So, maybe I need to model both the hop distance and the remaining distance.Let me try to structure this:- **Initial position:** 0- **Goal:** 1- **Hop 1:** 1/4 of the distance to the goal, so 1/4. Remaining distance: 1 - 1/4 = 3/4.- **Hop 2:** 1/4 of the remaining distance, which is 1/4 * 3/4 = 3/16. But his efficiency decreases by 3/4, so the actual hop is 3/16 * 3/4 = 9/64. Remaining distance: 3/4 - 9/64 = 48/64 - 9/64 = 39/64.- **Hop 3:** 1/4 of the remaining distance, which is 1/4 * 39/64 = 39/256. Efficiency decreases by 3/4, so hop distance is 39/256 * 3/4 = 117/1024. Remaining distance: 39/64 - 117/1024 = (624/1024 - 117/1024) = 507/1024.- **Hop 4:** 1/4 of 507/1024 = 507/4096. Efficiency decreases by 3/4, so hop distance is 507/4096 * 3/4 = 1521/16384. Remaining distance: 507/1024 - 1521/16384 = (8112/16384 - 1521/16384) = 6591/16384.- **Hop 5:** 1/4 of 6591/16384 = 6591/65536. Efficiency decreases by 3/4, so hop distance is 6591/65536 * 3/4 = 19773/262144. Remaining distance: 6591/16384 - 19773/262144 = (105456/262144 - 19773/262144) = 85683/262144.- **Hop 6:** 1/4 of 85683/262144 = 85683/1048576. Efficiency decreases by 3/4, so hop distance is 85683/1048576 * 3/4 = 257049/4194304. Remaining distance: 85683/262144 - 257049/4194304 = (1370928/4194304 - 257049/4194304) = 1113879/4194304.Wait, this seems complicated. Maybe there's a pattern or a formula I can use instead of calculating each hop step by step.Let me think about the total distance hopped after six hops. Each hop is 1/4 of the remaining distance, but each time, the efficiency is multiplied by 3/4. So, the hop distances form a geometric series where each term is (1/4)*(3/4)^(n-1), where n is the hop number.So, the total distance hopped after six hops would be the sum of the first six terms of this geometric series.The formula for the sum of the first n terms of a geometric series is S_n = a1*(1 - r^n)/(1 - r), where a1 is the first term and r is the common ratio.Here, a1 = 1/4, r = 3/4, and n = 6.So, S_6 = (1/4)*(1 - (3/4)^6)/(1 - 3/4) = (1/4)*(1 - 729/4096)/(1/4) = (1/4)*(3367/4096)/(1/4) = 3367/4096.Wait, that can't be right because 3367/4096 is approximately 0.82, but after six hops, he should be closer to 1. Maybe I made a mistake in the formula.Wait, no, because each hop is 1/4 of the remaining distance, but the remaining distance is also decreasing each time. So, the hop distances are not simply a geometric series with ratio 3/4. The remaining distance after each hop affects the next hop's distance.Hmm, maybe I need to model it differently. Let me denote the remaining distance after n hops as R_n. Then, the hop distance on the (n+1)th hop is (1/4)*R_n, and R_{n+1} = R_n - (1/4)*R_n = (3/4)*R_n.But wait, the efficiency also decreases by 3/4 each time. So, the hop distance is (1/4)*R_n*(3/4)^n?Wait, no, maybe the hop distance is (1/4)*R_n, and R_{n+1} = R_n - (1/4)*R_n = (3/4)*R_n. So, the remaining distance after each hop is multiplied by 3/4. Therefore, the hop distances are:Hop 1: (1/4)*1 = 1/4Hop 2: (1/4)*(3/4) = 3/16Hop 3: (1/4)*(3/4)^2 = 9/64Hop 4: (1/4)*(3/4)^3 = 27/256Hop 5: (1/4)*(3/4)^4 = 81/1024Hop 6: (1/4)*(3/4)^5 = 243/4096So, the total distance hopped after six hops is the sum of these six terms.Let me calculate each term:1. 1/4 = 1024/40962. 3/16 = 768/40963. 9/64 = 576/40964. 27/256 = 432/40965. 81/1024 = 324/40966. 243/4096 = 243/4096Now, adding them up:1024 + 768 = 17921792 + 576 = 23682368 + 432 = 28002800 + 324 = 31243124 + 243 = 3367So, total distance hopped is 3367/4096.Wait, but earlier I thought that was the sum, but I was confused because it seemed too low. But actually, 3367/4096 is approximately 0.82, which seems reasonable after six hops, considering each hop is getting smaller.But let me double-check. The sum of the series is S = (1/4)*(1 - (3/4)^6)/(1 - 3/4) = (1/4)*(1 - 729/4096)/(1/4) = (1/4)*(3367/4096)/(1/4) = 3367/4096.Yes, that matches. So, the total distance hopped after six hops is 3367/4096.Wait, but in the initial step-by-step calculation, I got a different result. Let me see where I went wrong.In the initial step-by-step, I was calculating each hop as (1/4)*(3/4)^(n-1), which is correct, but when I added them up, I think I made a mistake in the denominators.Wait, no, when I converted each hop to 4096 denominator, I added them correctly:1/4 = 1024/40963/16 = 768/40969/64 = 576/409627/256 = 432/409681/1024 = 324/4096243/4096 = 243/4096Adding these: 1024 + 768 = 1792; 1792 + 576 = 2368; 2368 + 432 = 2800; 2800 + 324 = 3124; 3124 + 243 = 3367. So, 3367/4096 is correct.But wait, in the initial problem, the user mentioned that the efficiency decreases by a factor of 3/4 with each hop. So, does that mean that each hop is 3/4 of the previous hop's distance? Or is it that the efficiency (the fraction of the remaining distance) decreases by 3/4 each time?I think I interpreted it correctly as each hop being 1/4 of the remaining distance, and the efficiency (the fraction) decreasing by 3/4 each time, meaning each hop is (1/4)*(3/4)^(n-1).But let me confirm with the problem statement: "each subsequent hop can only cover 1/4 of the remaining distance to the goal, and his efficiency to cover that fraction decreases by a factor of 3/4 with each hop."So, it's two separate factors: each hop is 1/4 of the remaining distance, and the efficiency (the fraction he can cover) decreases by 3/4 each time. So, the hop distance is (1/4)*(3/4)^(n-1).Therefore, the total distance is the sum of the first six terms of this series, which is 3367/4096.But wait, in the initial calculation, I thought the remaining distance after each hop is multiplied by 3/4, which is correct because he covers 1/4 of it, leaving 3/4. So, the remaining distance after n hops is (3/4)^n. Therefore, the hop distances are (1/4)*(3/4)^(n-1).So, the sum is S = (1/4)*(1 - (3/4)^6)/(1 - 3/4) = (1/4)*(1 - 729/4096)/(1/4) = 3367/4096.Yes, that seems correct. So, the total distance hopped after six hops is 3367/4096.Wait, but in the initial step-by-step, I had a different approach where I calculated each hop as (1/4)*(3/4)^(n-1) and added them up, getting 3367/4096. So, that's consistent.Therefore, the answer should be 3367/4096.But let me check if that's the simplest form. 3367 and 4096. 4096 is 2^12. 3367 divided by 7 is 481, which is a prime number. So, 3367 = 7*481. 4096 is 2^12, so no common factors. Therefore, 3367/4096 is already in simplest form.So, the final answer is 3367/4096.
❓Given a circle passing through the points (4,2) and (-2,-6), the sum of the four intercepts on the two coordinate axes is -2. Find the standard equation of the circle.
💡Alright, so I have this problem here about finding the standard equation of a circle. The circle passes through two points: (4,2) and (-2,-6). Also, the sum of the four intercepts on the two coordinate axes is -2. Hmm, okay, let me try to figure this out step by step.First, I remember that the general equation of a circle is something like (x^2 + y^2 + Dx + Ey + F = 0). I think D, E, and F are constants that we need to find. Since the circle passes through the points (4,2) and (-2,-6), I can plug these points into the general equation to get two equations.Let me do that. Plugging in (4,2):(4^2 + 2^2 + D*4 + E*2 + F = 0)That simplifies to:(16 + 4 + 4D + 2E + F = 0)Which is:(20 + 4D + 2E + F = 0)Okay, so that's equation (1): (4D + 2E + F = -20)Now, plugging in (-2,-6):((-2)^2 + (-6)^2 + D*(-2) + E*(-6) + F = 0)That simplifies to:(4 + 36 - 2D - 6E + F = 0)Which is:(40 - 2D - 6E + F = 0)So that's equation (2): (-2D - 6E + F = -40)Now, I have two equations:1. (4D + 2E + F = -20)2. (-2D - 6E + F = -40)I need a third equation because there are three unknowns: D, E, and F. The problem mentions the sum of the four intercepts on the two coordinate axes is -2. Hmm, intercepts... So, the x-intercepts and y-intercepts.For the x-intercepts, we set y=0 in the circle equation:(x^2 + Dx + F = 0)Similarly, for the y-intercepts, we set x=0:(y^2 + Ey + F = 0)So, the x-intercepts are the solutions to (x^2 + Dx + F = 0), and the y-intercepts are the solutions to (y^2 + Ey + F = 0).If I let the x-intercepts be (x_1) and (x_2), then from quadratic equation properties, (x_1 + x_2 = -D).Similarly, for the y-intercepts (y_1) and (y_2), (y_1 + y_2 = -E).The sum of all four intercepts is (x_1 + x_2 + y_1 + y_2 = -D + (-E) = - (D + E)).According to the problem, this sum is -2. So:(- (D + E) = -2)Which simplifies to:(D + E = 2)That's equation (3): (D + E = 2)Now, I have three equations:1. (4D + 2E + F = -20)2. (-2D - 6E + F = -40)3. (D + E = 2)Let me try to solve these equations.From equation (3), I can express D in terms of E: (D = 2 - E)Now, substitute D into equations (1) and (2).Substituting into equation (1):(4*(2 - E) + 2E + F = -20)Simplify:(8 - 4E + 2E + F = -20)Combine like terms:(8 - 2E + F = -20)Subtract 8 from both sides:(-2E + F = -28)Let me call this equation (4): (-2E + F = -28)Now, substitute D into equation (2):(-2*(2 - E) - 6E + F = -40)Simplify:(-4 + 2E - 6E + F = -40)Combine like terms:(-4 - 4E + F = -40)Add 4 to both sides:(-4E + F = -36)Let me call this equation (5): (-4E + F = -36)Now, I have two equations:4. (-2E + F = -28)5. (-4E + F = -36)Let me subtract equation (4) from equation (5):((-4E + F) - (-2E + F) = -36 - (-28))Simplify:(-4E + F + 2E - F = -36 + 28)Combine like terms:(-2E = -8)Divide both sides by -2:(E = 4)Now, substitute E = 4 into equation (3): (D + 4 = 2), so (D = -2)Now, substitute E = 4 into equation (4): (-2*4 + F = -28)Which is:(-8 + F = -28)Add 8 to both sides:(F = -20)So, D = -2, E = 4, F = -20Therefore, the general equation of the circle is:(x^2 + y^2 - 2x + 4y - 20 = 0)To write this in standard form, I need to complete the squares for x and y.Starting with x terms: (x^2 - 2x). To complete the square, take half of -2, which is -1, square it to get 1.Similarly, for y terms: (y^2 + 4y). Half of 4 is 2, square it to get 4.So, add and subtract these squares:(x^2 - 2x + 1 - 1 + y^2 + 4y + 4 - 4 - 20 = 0)Simplify:((x - 1)^2 - 1 + (y + 2)^2 - 4 - 20 = 0)Combine constants:((x - 1)^2 + (y + 2)^2 - 25 = 0)Move the constant to the other side:((x - 1)^2 + (y + 2)^2 = 25)So, the standard equation of the circle is ((x - 1)^2 + (y + 2)^2 = 25)Let me double-check if this makes sense. The center is at (1, -2), and the radius is 5. Let's see if the points (4,2) and (-2,-6) lie on this circle.For (4,2):((4 - 1)^2 + (2 + 2)^2 = 3^2 + 4^2 = 9 + 16 = 25). Yes, that works.For (-2,-6):((-2 - 1)^2 + (-6 + 2)^2 = (-3)^2 + (-4)^2 = 9 + 16 = 25). That also works.Now, checking the intercepts. For x-intercepts, set y=0:((x - 1)^2 + (0 + 2)^2 = 25)((x - 1)^2 + 4 = 25)((x - 1)^2 = 21)So, (x - 1 = pm sqrt{21}), which gives (x = 1 pm sqrt{21})Sum of x-intercepts: (1 + sqrt{21} + 1 - sqrt{21} = 2)For y-intercepts, set x=0:((0 - 1)^2 + (y + 2)^2 = 25)(1 + (y + 2)^2 = 25)((y + 2)^2 = 24)So, (y + 2 = pm sqrt{24}), which gives (y = -2 pm 2sqrt{6})Sum of y-intercepts: (-2 + 2sqrt{6} + (-2 - 2sqrt{6}) = -4)Total sum of intercepts: 2 + (-4) = -2, which matches the given condition.Alright, everything checks out!
❓Petya marked point (X) on edge (AB) of cube (ABCDA_1B_1C_1D_1), which divides edge (AB) in the ratio (1:2) from vertex (A). Provide an example where Petya can mark points (Y) on edge (CC_1) and (Z) on edge (A_1D_1) such that triangle (XYZ) is equilateral. Justify your answer.
💡Alright, so I've got this geometry problem here about a cube and marking points to form an equilateral triangle. Let me try to wrap my head around it step by step.First, the cube is labeled ABCDA₁B₁C₁D₁. I remember that in cube notation, the vertices are labeled such that ABCD is the base face, and A₁B₁C₁D₁ is the top face, with edges connecting corresponding vertices. So, A is connected to A₁, B to B₁, and so on.Petya marked a point X on edge AB, dividing it in the ratio 1:2 from vertex A. That means AX:XB = 1:2. If I consider the edge AB to have a length of, say, 3 units for simplicity, then AX would be 1 unit and XB would be 2 units. This makes sense because 1:2 is a ratio that adds up to 3, which is the total length of AB.Now, the task is to find points Y on edge CC₁ and Z on edge A₁D₁ such that triangle XYZ is equilateral. An equilateral triangle has all sides equal and all angles equal to 60 degrees. So, I need to ensure that the distances XY, YZ, and ZX are all equal.Let me visualize the cube. Since X is on AB, Y is on CC₁, and Z is on A₁D₁, these points are on different edges, some on the base and some on the top face. I need to figure out where exactly to place Y and Z so that the triangle formed is equilateral.I think assigning coordinates might help here. Let's place the cube in a 3D coordinate system where point A is at the origin (0,0,0). Then, since it's a cube, all edges are of equal length. Let's assume each edge has length 3 units for simplicity, as I mentioned earlier.So, the coordinates of the vertices would be:- A: (0,0,0)- B: (3,0,0)- C: (3,3,0)- D: (0,3,0)- A₁: (0,0,3)- B₁: (3,0,3)- C₁: (3,3,3)- D₁: (0,3,3)Given that, point X is on AB, 1 unit from A. So, moving 1 unit along AB from A, which is along the x-axis, X would be at (1,0,0).Now, I need to find points Y on CC₁ and Z on A₁D₁ such that triangle XYZ is equilateral. Let's denote the coordinates of Y and Z.Point Y is on CC₁. Since C is at (3,3,0) and C₁ is at (3,3,3), Y must have coordinates (3,3,k) where k is between 0 and 3.Similarly, point Z is on A₁D₁. A₁ is at (0,0,3) and D₁ is at (0,3,3), so Z must have coordinates (0,m,3) where m is between 0 and 3.So, our points are:- X: (1,0,0)- Y: (3,3,k)- Z: (0,m,3)We need to find k and m such that the distances XY, YZ, and ZX are equal.Let's compute the distances using the distance formula in 3D.First, distance XY:XY = sqrt[(3-1)^2 + (3-0)^2 + (k-0)^2] = sqrt[(2)^2 + (3)^2 + k^2] = sqrt[4 + 9 + k^2] = sqrt[13 + k^2]Next, distance YZ:YZ = sqrt[(0-3)^2 + (m-3)^2 + (3 - k)^2] = sqrt[(-3)^2 + (m-3)^2 + (3 - k)^2] = sqrt[9 + (m-3)^2 + (3 - k)^2]Distance ZX:ZX = sqrt[(1-0)^2 + (0 - m)^2 + (0 - 3)^2] = sqrt[(1)^2 + (-m)^2 + (-3)^2] = sqrt[1 + m^2 + 9] = sqrt[10 + m^2]So, we have:XY = sqrt(13 + k^2)YZ = sqrt[9 + (m - 3)^2 + (3 - k)^2]ZX = sqrt(10 + m^2)We need all three distances to be equal. Therefore, we can set up equations:1. sqrt(13 + k^2) = sqrt(10 + m^2)2. sqrt(13 + k^2) = sqrt[9 + (m - 3)^2 + (3 - k)^2]Let's square both sides of the first equation to eliminate the square roots:13 + k^2 = 10 + m^2=> m^2 = 13 + k^2 - 10=> m^2 = 3 + k^2=> m = sqrt(3 + k^2) [Since m is a length, we take the positive root]Now, let's square both sides of the second equation:13 + k^2 = 9 + (m - 3)^2 + (3 - k)^2Let's expand the right-hand side:= 9 + (m^2 - 6m + 9) + (9 - 6k + k^2)= 9 + m^2 - 6m + 9 + 9 - 6k + k^2= 9 + 9 + 9 + m^2 + k^2 - 6m - 6k= 27 + m^2 + k^2 - 6m - 6kSo, the equation becomes:13 + k^2 = 27 + m^2 + k^2 - 6m - 6kSimplify by subtracting 13 + k^2 from both sides:0 = 14 + m^2 - 6m - 6kBut from the first equation, we have m^2 = 3 + k^2. Let's substitute that into this equation:0 = 14 + (3 + k^2) - 6m - 6k0 = 17 + k^2 - 6m - 6kNow, let's rearrange:k^2 - 6k - 6m + 17 = 0But we also have m = sqrt(3 + k^2). Let's substitute m into this equation:k^2 - 6k - 6*sqrt(3 + k^2) + 17 = 0This looks a bit complicated, but maybe we can solve for k numerically or look for integer solutions.Let me try to see if k is an integer. Let's test k=1:1 - 6 - 6*sqrt(4) + 17 = 1 -6 -12 +17 = 0. Hey, that works!So, k=1.Then, m = sqrt(3 + 1^2) = sqrt(4) = 2.So, k=1 and m=2.Therefore, point Y is at (3,3,1) and point Z is at (0,2,3).Let me verify the distances:XY: sqrt[(3-1)^2 + (3-0)^2 + (1-0)^2] = sqrt[4 + 9 + 1] = sqrt[14]YZ: sqrt[(0-3)^2 + (2-3)^2 + (3 - 1)^2] = sqrt[9 + 1 + 4] = sqrt[14]ZX: sqrt[(1-0)^2 + (0 - 2)^2 + (0 - 3)^2] = sqrt[1 + 4 + 9] = sqrt[14]Yes, all sides are equal to sqrt(14), so triangle XYZ is indeed equilateral.So, the points are:- X: (1,0,0)- Y: (3,3,1)- Z: (0,2,3)This satisfies the condition.**Final Answer**boxed{XYZ text{ is equilateral when } Y text{ is one-third along } CC_1 text{ and } Z text{ is two-thirds along } A_1D_1.}
❓In Skyline Hospital one year, the multiple-birth statistics reported sets of twins, triplets, and quadruplets totaling 1200 babies. There were five times as many sets of triplets as sets of quadruplets, and there were three times as many sets of twins as sets of triplets. How many of these 1200 babies were in sets of quadruplets?A) 90B) 95C) 98D) 100E) 105
💡First, define the variables:- Let ( c ) represent the number of sets of quadruplets.- The number of sets of triplets is ( 5c ) (five times as many as quadruplets).- The number of sets of twins is ( 3 times 5c = 15c ) (three times as many as triplets).Next, calculate the total number of babies:- Babies from twins: ( 2 times 15c = 30c )- Babies from triplets: ( 3 times 5c = 15c )- Babies from quadruplets: ( 4c )Set up the equation for the total number of babies:[30c + 15c + 4c = 1200][49c = 1200][c = frac{1200}{49} approx 24.49]Finally, calculate the number of babies in sets of quadruplets:[4c = 4 times 24.49 approx 98]
❓Suppose that sec x + tan x = frac{15}{4} and csc x + cot x = frac{p}{q}, where frac{p}{q} is in lowest terms. Find p+q.
💡Alright, so I have this problem where I'm given that sec x + tan x equals 15/4, and I need to find csc x + cot x in the form p/q, where p and q are coprime integers, and then find p + q. Hmm, okay. Let me try to figure this out step by step.First, I remember that sec x is 1/cos x and tan x is sin x / cos x. So, maybe I can express sec x + tan x in terms of sin x and cos x. Let me write that down:sec x + tan x = 1/cos x + sin x / cos x = (1 + sin x) / cos x.So, (1 + sin x) / cos x = 15/4. That gives me an equation involving sin x and cos x. Maybe I can solve for sin x or cos x.Let me denote sin x as s and cos x as c to make it simpler. So, the equation becomes:(1 + s) / c = 15/4.Which implies that 1 + s = (15/4) c.Okay, so 1 + s = (15/4) c. I can write this as:s = (15/4) c - 1.Now, I also know that sin^2 x + cos^2 x = 1. So, s^2 + c^2 = 1. Maybe I can substitute s from the previous equation into this identity.Let me do that:[(15/4) c - 1]^2 + c^2 = 1.Expanding the square:(225/16)c^2 - (30/4)c + 1 + c^2 = 1.Simplify the terms:225/16 c^2 - 30/4 c + 1 + c^2 = 1.Combine like terms:(225/16 + 16/16) c^2 - (30/4)c + 1 = 1.So, (241/16)c^2 - (30/4)c + 1 = 1.Subtract 1 from both sides:241/16 c^2 - 30/4 c = 0.Factor out c:c (241/16 c - 30/4) = 0.So, either c = 0 or 241/16 c - 30/4 = 0.But c = cos x, and if c = 0, then sec x would be undefined, which contradicts the given equation. So, c ≠ 0. Therefore, we can solve for c:241/16 c = 30/4.Multiply both sides by 16:241 c = (30/4) * 16.Simplify 30/4 * 16: 30/4 is 15/2, and 15/2 * 16 is 15 * 8 = 120.So, 241 c = 120.Therefore, c = 120 / 241.Okay, so cos x is 120/241. Now, let's find sin x using the equation s = (15/4)c - 1.So, s = (15/4)(120/241) - 1.Calculate (15/4)(120/241):15 * 120 = 1800.4 * 241 = 964.So, 1800 / 964. Let me simplify that fraction.Divide numerator and denominator by 4: 1800 ÷ 4 = 450, 964 ÷ 4 = 241.So, 450/241.Therefore, s = 450/241 - 1.Convert 1 to 241/241:s = 450/241 - 241/241 = (450 - 241)/241 = 209/241.So, sin x = 209/241.Alright, so now I have sin x and cos x:sin x = 209/241,cos x = 120/241.Now, I need to find csc x + cot x.csc x is 1/sin x, and cot x is cos x / sin x.So, csc x + cot x = 1/sin x + cos x / sin x = (1 + cos x) / sin x.So, let's compute that:(1 + cos x) / sin x = (1 + 120/241) / (209/241).First, compute 1 + 120/241:1 is 241/241, so 241/241 + 120/241 = 361/241.So, numerator is 361/241, denominator is 209/241.Therefore, (361/241) / (209/241) = 361/209.Simplify 361/209.Let me check if 361 and 209 have any common factors.209 factors: 11 * 19.361 is 19^2.So, 361 = 19 * 19,209 = 11 * 19.So, common factor is 19.Divide numerator and denominator by 19:361 ÷ 19 = 19,209 ÷ 19 = 11.So, simplified fraction is 19/11.Therefore, csc x + cot x = 19/11.So, p = 19, q = 11. Therefore, p + q = 19 + 11 = 30.Wait, but in the initial problem statement, the user mentioned that the answer was 390, but that seems incorrect because 19 + 11 is 30. Maybe I made a mistake somewhere.Let me double-check my calculations.Starting from sec x + tan x = 15/4.Expressed as (1 + sin x)/cos x = 15/4.So, 1 + sin x = (15/4) cos x.Then, sin x = (15/4) cos x - 1.Then, sin^2 x + cos^2 x = 1.Substituting sin x:[(15/4 cos x - 1)]^2 + cos^2 x = 1.Expanding:(225/16 cos^2 x - 30/4 cos x + 1) + cos^2 x = 1.Combine like terms:(225/16 + 16/16) cos^2 x - 30/4 cos x + 1 = 1.So, 241/16 cos^2 x - 30/4 cos x = 0.Factor out cos x:cos x (241/16 cos x - 30/4) = 0.So, cos x = 0 or 241/16 cos x = 30/4.cos x = 0 is rejected, so 241/16 cos x = 30/4.Multiply both sides by 16: 241 cos x = 120.So, cos x = 120/241.Then, sin x = (15/4)(120/241) - 1.Compute (15/4)(120/241):15 * 120 = 1800,4 * 241 = 964,So, 1800/964 simplifies to 450/241.Then, sin x = 450/241 - 1 = 450/241 - 241/241 = 209/241.So, sin x = 209/241.Then, csc x + cot x = (1 + cos x)/sin x.1 + cos x = 1 + 120/241 = 361/241.Divide by sin x: (361/241)/(209/241) = 361/209.Simplify 361/209: both divisible by 19.361 ÷ 19 = 19,209 ÷ 19 = 11.So, 19/11.Therefore, p = 19, q = 11, p + q = 30.Hmm, so I think the initial thought process had an error where it concluded 390, but actually, the correct answer is 30. Maybe the initial user made a mistake in their calculation.Alternatively, perhaps I made a mistake in interpreting the problem. Let me check again.Wait, the problem says "csc x + cot x = p/q". I computed that as 19/11, which is in lowest terms, so p + q = 30.Alternatively, maybe I should have considered another identity or approach.Wait, another approach: I remember that if sec x + tan x = 15/4, then sec x - tan x is the reciprocal of that, because (sec x + tan x)(sec x - tan x) = sec^2 x - tan^2 x = 1.So, if sec x + tan x = 15/4, then sec x - tan x = 4/15.Therefore, we can solve for sec x and tan x.Let me write:sec x + tan x = 15/4,sec x - tan x = 4/15.Adding these two equations:2 sec x = 15/4 + 4/15.Compute 15/4 + 4/15:Find a common denominator, which is 60.15/4 = 225/60,4/15 = 16/60.So, 225/60 + 16/60 = 241/60.Therefore, 2 sec x = 241/60,So, sec x = 241/120.Therefore, cos x = 120/241, which matches what I found earlier.Then, subtracting the two equations:(sec x + tan x) - (sec x - tan x) = 15/4 - 4/15.So, 2 tan x = 15/4 - 4/15.Compute 15/4 - 4/15:Again, common denominator 60.15/4 = 225/60,4/15 = 16/60.So, 225/60 - 16/60 = 209/60.Therefore, 2 tan x = 209/60,So, tan x = 209/120.Which is the same as sin x / cos x = 209/120.Since cos x = 120/241, sin x = (209/120) * (120/241) = 209/241, which is consistent.So, everything checks out.Therefore, csc x + cot x = (1 + cos x)/sin x = (1 + 120/241)/(209/241) = (361/241)/(209/241) = 361/209 = 19/11.So, p = 19, q = 11, p + q = 30.Therefore, the answer is 30.**Final Answer**boxed{30}
❓For the function f(x)=frac{1}{3}|x^3|-frac{a}{2}x^2+(3-a)|x|+b, there are six different monotonic intervals. Then, the range of a is __________.
💡Okay, let's try to figure out the range of ( a ) for which the function ( f(x) = frac{1}{3}|x^3| - frac{a}{2}x^2 + (3 - a)|x| + b ) has six different monotonic intervals. Hmm, that sounds a bit complicated, but I'll take it step by step.First, I remember that the number of monotonic intervals a function has is related to the number of critical points it has. Critical points occur where the derivative is zero or undefined. So, I think I need to find the derivative of ( f(x) ) and analyze its roots.But before that, I notice that the function has absolute value terms, specifically ( |x^3| ) and ( |x| ). Absolute value functions can complicate things because they introduce corners or points where the derivative might not exist. However, since ( |x^3| ) is actually equal to ( |x|^3 ), which is smooth everywhere except at ( x = 0 ), but since it's a higher power, maybe it's differentiable there too? Hmm, not sure. Maybe I should consider the function for ( x geq 0 ) and ( x < 0 ) separately because of the absolute values.Wait, the function is given as ( f(x) = frac{1}{3}|x^3| - frac{a}{2}x^2 + (3 - a)|x| + b ). Let me see if this function is even or odd. Plugging in ( -x ) into the function:( f(-x) = frac{1}{3}|(-x)^3| - frac{a}{2}(-x)^2 + (3 - a)|-x| + b )Simplify each term:- ( |(-x)^3| = | -x^3 | = |x^3| )- ( (-x)^2 = x^2 )- ( |-x| = |x| )So, ( f(-x) = frac{1}{3}|x^3| - frac{a}{2}x^2 + (3 - a)|x| + b = f(x) )Oh, so ( f(x) ) is an even function. That means it's symmetric about the y-axis. Therefore, the behavior of the function for ( x > 0 ) will mirror that for ( x < 0 ). So, if I can figure out the number of monotonic intervals for ( x > 0 ), I can double it (or adjust accordingly) for the entire function.The problem states there are six different monotonic intervals. Since the function is even, that suggests that for ( x > 0 ), there are three monotonic intervals, and similarly for ( x < 0 ). So, I need to focus on ( x > 0 ) and find when the derivative has two critical points, leading to three intervals.Let me compute the derivative ( f'(x) ) for ( x > 0 ). Since for ( x > 0 ), ( |x^3| = x^3 ) and ( |x| = x ). So, the function simplifies to:( f(x) = frac{1}{3}x^3 - frac{a}{2}x^2 + (3 - a)x + b )Now, take the derivative:( f'(x) = frac{d}{dx}left( frac{1}{3}x^3 - frac{a}{2}x^2 + (3 - a)x + b right) )( f'(x) = x^2 - a x + (3 - a) )So, ( f'(x) = x^2 - a x + (3 - a) ). To find critical points, set ( f'(x) = 0 ):( x^2 - a x + (3 - a) = 0 )This is a quadratic equation in ( x ). For there to be two distinct critical points (which would lead to three monotonic intervals on ( x > 0 )), the quadratic must have two distinct real roots. The condition for that is that the discriminant is positive.The discriminant ( D ) of ( x^2 - a x + (3 - a) = 0 ) is:( D = (-a)^2 - 4 times 1 times (3 - a) )( D = a^2 - 12 + 4a )( D = a^2 + 4a - 12 )For two distinct real roots, ( D > 0 ):( a^2 + 4a - 12 > 0 )Let me solve this inequality. First, find the roots of the quadratic equation ( a^2 + 4a - 12 = 0 ):Using quadratic formula:( a = frac{ -4 pm sqrt{16 + 48} }{2} )( a = frac{ -4 pm sqrt{64} }{2} )( a = frac{ -4 pm 8 }{2} )So, two solutions:1. ( a = frac{ -4 + 8 }{2} = frac{4}{2} = 2 )2. ( a = frac{ -4 - 8 }{2} = frac{ -12 }{2} = -6 )So, the quadratic ( a^2 + 4a - 12 ) factors as ( (a - 2)(a + 6) ). To determine where it's positive, we can analyze the intervals determined by the roots ( a = -6 ) and ( a = 2 ).- For ( a < -6 ), say ( a = -7 ): ( (-7 - 2)(-7 + 6) = (-9)(-1) = 9 > 0 )- For ( -6 < a < 2 ), say ( a = 0 ): ( (0 - 2)(0 + 6) = (-2)(6) = -12 < 0 )- For ( a > 2 ), say ( a = 3 ): ( (3 - 2)(3 + 6) = (1)(9) = 9 > 0 )So, ( a^2 + 4a - 12 > 0 ) when ( a < -6 ) or ( a > 2 ).But wait, in our case, ( a ) is a parameter in the original function. Let me think about the context. The function ( f(x) ) has terms with ( a ) in coefficients, but I don't see any immediate restrictions on ( a ) except those imposed by the discriminant condition.However, I should also consider whether the critical points are positive because we're looking at ( x > 0 ). So, even if the quadratic has two real roots, they need to be positive for the critical points to lie in ( x > 0 ).So, let's recall that for a quadratic equation ( x^2 - a x + (3 - a) = 0 ), the sum of the roots is ( a ) and the product is ( 3 - a ).For both roots to be positive, we need:1. Sum of roots ( > 0 ): ( a > 0 )2. Product of roots ( > 0 ): ( 3 - a > 0 ) => ( a < 3 )So, combining these, we have ( 0 < a < 3 ).But from the discriminant condition, we have ( a > 2 ) or ( a < -6 ). So, intersecting these two conditions:- From discriminant: ( a > 2 ) or ( a < -6 )- From positivity of roots: ( 0 < a < 3 )Therefore, the overlap is ( 2 < a < 3 ).Wait, but what about ( a < -6 )? If ( a < -6 ), then the sum of roots is ( a ), which would be negative, but the product is ( 3 - a ). If ( a < -6 ), then ( 3 - a > 3 - (-6) = 9 > 0 ). So, the product is positive, but the sum is negative. That would mean both roots are negative because their sum is negative and product is positive. But since we're considering ( x > 0 ), negative roots don't affect the critical points in ( x > 0 ). So, for ( x > 0 ), we don't have any critical points if ( a < -6 ), which would mean the function is monotonic on ( x > 0 ). But the problem states there are six monotonic intervals, which implies three on each side of zero. So, if ( a < -6 ), we don't get three intervals on ( x > 0 ), so that's not acceptable.Therefore, the only valid range is ( 2 < a < 3 ).Wait, let me double-check. If ( a > 2 ), then from the discriminant, we have two real roots. From the sum and product, if ( a > 2 ), then sum is positive, product is ( 3 - a ). So, if ( a < 3 ), product is positive. So, when ( 2 < a < 3 ), both roots are positive, which is what we need for ( x > 0 ). If ( a = 3 ), the product becomes zero, so one root is zero, but since we're considering ( x > 0 ), that would mean a critical point at zero, but since we're already considering ( x > 0 ), maybe it's a boundary case. Similarly, if ( a > 3 ), the product becomes negative, so one root is positive and one is negative. But since we're only considering ( x > 0 ), only one critical point there, leading to two monotonic intervals on ( x > 0 ), which would result in four total intervals (two on each side), but the problem says six, so ( a > 3 ) is also invalid.Similarly, if ( a = 2 ), discriminant is zero, so only one critical point on ( x > 0 ), leading to two intervals on ( x > 0 ), again not enough.So, putting it all together, the range of ( a ) is ( 2 < a < 3 ).**Final Answer**The range of ( a ) is boxed{(2, 3)}.