Swirling vortex

Calculus Level 3

The area bounded by the curve 2 y 2 = x 2y^2 = x and the line 4 y = x 4y = x is rotated around the y-axis. What is the volume of the resulting structure?


The answer is 53.61646933333332754045841284096240997314453125.

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1 solution

Tunk-Fey Ariawan
Jan 31, 2014

First, we obtain the intersection points 2 y 2 = 4 y y 2 2 y = 0 y ( y 2 ) = 0 y = 0 or y = 2. \begin{aligned} 2y^2&=4y\\ y^2-2y&=0\\ y(y-2)&=0\\ y&=0 \,\text{ or }\, y=2. \end{aligned} Thus, the volume is V = π 0 2 ( ( 4 y ) 2 ( 2 y 2 ) 2 ) d y = π 0 2 ( 16 y 2 4 y 4 ) d y = π ( 16 3 y 3 4 5 y 5 ) 0 2 = 256 15 π 53.6165 \begin{aligned} V&=\pi\int_0^2 \left((4y)^2-(2y^2)^2\right)\,dy\\ &=\pi\int_0^2 \left(16y^2-4y^4\right)\,dy\\ &=\pi\left.\left(\frac{16}{3}y^3-\frac{4}{5}y^5\right)\right|_0^2\\ &=\frac{256}{15}\pi\\ &\approx\boxed{53.6165} \end{aligned} # Q . E . D . # \text{\# }\mathbb{Q}.\mathbb{E}.\mathbb{D}.\text{\#}

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