The problem asks to find the volume of the solid generated by revolving the region bounded by the curves $y = 3 - x$ and $y = x^2 + 1$ about the x-axis.

AnalysisCalculusVolume of RevolutionIntegrationWasher Method
2025/6/28

1. Problem Description

The problem asks to find the volume of the solid generated by revolving the region bounded by the curves y=3xy = 3 - x and y=x2+1y = x^2 + 1 about the x-axis.

2. Solution Steps

First, find the points of intersection of the two curves by setting them equal to each other:
3x=x2+13 - x = x^2 + 1
x2+x2=0x^2 + x - 2 = 0
(x+2)(x1)=0(x+2)(x-1) = 0
x=2x = -2 or x=1x = 1
So the intersection points are at x=2x = -2 and x=1x = 1.
Now, we use the washer method to find the volume. The formula for the washer method is:
V=πab(R(x)2r(x)2)dxV = \pi \int_a^b (R(x)^2 - r(x)^2) dx
where R(x)R(x) is the outer radius and r(x)r(x) is the inner radius.
In this case, R(x)=3xR(x) = 3 - x and r(x)=x2+1r(x) = x^2 + 1. The limits of integration are a=2a = -2 and b=1b = 1.
So the volume is:
V=π21((3x)2(x2+1)2)dxV = \pi \int_{-2}^1 ((3 - x)^2 - (x^2 + 1)^2) dx
V=π21(96x+x2(x4+2x2+1))dxV = \pi \int_{-2}^1 (9 - 6x + x^2 - (x^4 + 2x^2 + 1)) dx
V=π21(96x+x2x42x21)dxV = \pi \int_{-2}^1 (9 - 6x + x^2 - x^4 - 2x^2 - 1) dx
V=π21(x4x26x+8)dxV = \pi \int_{-2}^1 (-x^4 - x^2 - 6x + 8) dx
V=π[x55x333x2+8x]21V = \pi [-\frac{x^5}{5} - \frac{x^3}{3} - 3x^2 + 8x]_{-2}^1
V=π[(15133+8)((2)55(2)333(2)2+8(2))]V = \pi [(-\frac{1}{5} - \frac{1}{3} - 3 + 8) - (-\frac{(-2)^5}{5} - \frac{(-2)^3}{3} - 3(-2)^2 + 8(-2))]
V=π[(1513+5)(325+831216)]V = \pi [(-\frac{1}{5} - \frac{1}{3} + 5) - (\frac{32}{5} + \frac{8}{3} - 12 - 16)]
V=π[(1513+5)(325+8328)]V = \pi [(-\frac{1}{5} - \frac{1}{3} + 5) - (\frac{32}{5} + \frac{8}{3} - 28)]
V=π[1513+532583+28]V = \pi [-\frac{1}{5} - \frac{1}{3} + 5 - \frac{32}{5} - \frac{8}{3} + 28]
V=π[33593+33]V = \pi [-\frac{33}{5} - \frac{9}{3} + 33]
V=π[3353+33]V = \pi [-\frac{33}{5} - 3 + 33]
V=π[335+30]V = \pi [-\frac{33}{5} + 30]
V=π[335+1505]V = \pi [-\frac{33}{5} + \frac{150}{5}]
V=π[1175]V = \pi [\frac{117}{5}]
V=117π5V = \frac{117\pi}{5}

3. Final Answer

The volume of the solid is 117π5\frac{117\pi}{5}.

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