The problem asks to evaluate the definite integral $2\pi \int_{0}^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{1 + (\frac{150y^2 - 4y}{80\sqrt{y^3(50-y)}})^2} dy$.

AnalysisDefinite IntegralSurface Area of RevolutionCalculusIntegration
2025/5/8

1. Problem Description

The problem asks to evaluate the definite integral
2π050(12+y3(50y)40)1+(150y24y80y3(50y))2dy2\pi \int_{0}^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{1 + (\frac{150y^2 - 4y}{80\sqrt{y^3(50-y)}})^2} dy.

2. Solution Steps

Let f(y)=12+y3(50y)40f(y) = 12 + \frac{\sqrt{y^3(50-y)}}{40}.
We need to find f(y)f'(y) to simplify the expression under the square root in the integral.
f(y)=12+(y3(50y))1/240=12+(50y3y4)1/240f(y) = 12 + \frac{(y^3(50-y))^{1/2}}{40} = 12 + \frac{(50y^3 - y^4)^{1/2}}{40}
f(y)=14012(50y3y4)1/2(150y24y3)=150y24y38050y3y4=150y24y380y3(50y)f'(y) = \frac{1}{40} \cdot \frac{1}{2} (50y^3 - y^4)^{-1/2} (150y^2 - 4y^3) = \frac{150y^2 - 4y^3}{80\sqrt{50y^3 - y^4}} = \frac{150y^2 - 4y^3}{80\sqrt{y^3(50-y)}}
Thus the integral becomes:
2π050f(y)1+(f(y))2dy=2π050(12+y3(50y)40)1+(150y24y380y3(50y))2dy2\pi \int_{0}^{50} f(y) \sqrt{1 + (f'(y))^2} dy = 2\pi \int_{0}^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{1 + (\frac{150y^2 - 4y^3}{80\sqrt{y^3(50-y)}})^2} dy
This looks like the surface area of revolution around the x-axis for the function f(y)f(y) from y=0y=0 to y=50y=50.
The formula for the surface area of revolution around the x-axis is given by
A=2πabf(y)1+(f(y))2dyA = 2\pi \int_a^b f(y) \sqrt{1 + (f'(y))^2} dy
where f(y)=12+y3(50y)40f(y) = 12 + \frac{\sqrt{y^3(50-y)}}{40}.
We can express the integral as
2π050(12+y3(50y)40)1+(150y24y380y3(50y))2dy=2π050(12+y3(50y)40)1+(150y24y3)26400y3(50y)dy2\pi \int_0^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{1 + (\frac{150y^2 - 4y^3}{80\sqrt{y^3(50-y)}})^2} dy = 2\pi \int_0^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{1 + \frac{(150y^2 - 4y^3)^2}{6400y^3(50-y)}} dy
=2π050(12+y3(50y)40)6400y3(50y)+(150y24y3)26400y3(50y)dy= 2\pi \int_0^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \sqrt{\frac{6400y^3(50-y) + (150y^2 - 4y^3)^2}{6400y^3(50-y)}} dy
=2π050(12+y3(50y)40)6400y3(50y)+(150y24y3)280y3(50y)dy= 2\pi \int_0^{50} (12 + \frac{\sqrt{y^3(50-y)}}{40}) \frac{\sqrt{6400y^3(50-y) + (150y^2 - 4y^3)^2}}{80\sqrt{y^3(50-y)}} dy
=2π050140(480+y3(50y))320000y36400y4+22500y41200y5+16y680y3(50y)dy= 2\pi \int_0^{50} \frac{1}{40}(480 + \sqrt{y^3(50-y)}) \frac{\sqrt{320000y^3 - 6400y^4 + 22500y^4 - 1200y^5 + 16y^6}}{80\sqrt{y^3(50-y)}} dy
This integral is too complicated to solve analytically.
Based on the information available, I cannot simplify the integral to a solvable form. Therefore, I can't compute the final answer.
However, the expression resembles the formula for the surface area obtained by revolving a curve defined by x=g(y)x = g(y) around the x-axis. In this case, the surface area formula is 2πabf(y)1+(f(y))2dy2\pi \int_a^b f(y) \sqrt{1 + (f'(y))^2} dy.
Therefore the integral can be seen as the surface area of the curve.

3. Final Answer

I am unable to provide a final numerical answer for this problem due to its complexity.

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