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astro's Question
Math
Posted 5 months ago
Compute the volume of the solid obtained by rotating the region bounded by y=x2y = x^2, x=0x = 0, and y=4y = 4 about the y-axis.
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Answer from Sia
Posted 5 months ago
Solution by Steps
step 1
To find the volume of the solid obtained by rotating the region bounded by y=x2y = x^2, x=0x = 0, and y=4y = 4 about the y-axis, we use the method of cylindrical shells
step 2
The height of a typical shell is given by h=y=x2h = y = x^2
step 3
The radius of a typical shell is r=xr = x
step 4
The volume of a typical shell is dV=2πxhdx=2πxx2dx=2πx3dxdV = 2 \pi x \cdot h \cdot dx = 2 \pi x \cdot x^2 \cdot dx = 2 \pi x^3 \cdot dx
step 5
To find the total volume, we integrate dVdV from x=0x = 0 to x=2x = 2 (since y=4y = 4 corresponds to x=2x = 2):
step 6
V=022πx3dxV = \int_{0}^{2} 2 \pi x^3 \, dx
step 7
Compute the integral:
step 8
V=2π02x3dx=2π[x44]02=2π(244044)=2π(164)=2π4=8πV = 2 \pi \int_{0}^{2} x^3 \, dx = 2 \pi \left[ \frac{x^4}{4} \right]_{0}^{2} = 2 \pi \left( \frac{2^4}{4} - \frac{0^4}{4} \right) = 2 \pi \left( \frac{16}{4} \right) = 2 \pi \cdot 4 = 8 \pi
Answer
The volume of the solid is 8π8 \pi.
Key Concept
Cylindrical Shells Method
Explanation
The cylindrical shells method is used to find the volume of a solid of revolution by integrating the volume of infinitesimally thin cylindrical shells.

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