Volume Rotation X 511B76
1. **Problem:** Find the volume of the solid obtained by rotating the region bounded by $y = 2 - \frac{1}{2}x$, $y=0$, $x=1$, and $x=2$ about the x-axis.
2. **Formula:** For rotation about the x-axis, the volume $V$ is given by the disk method:
$$V = \pi \int_a^b [f(x)]^2 \, dx$$
where $f(x)$ is the function defining the radius of the disk.
3. **Identify bounds and function:** Here, $f(x) = 2 - \frac{1}{2}x$, $a=1$, $b=2$.
4. **Set up the integral:**
$$V = \pi \int_1^2 \left(2 - \frac{1}{2}x\right)^2 \, dx$$
5. **Expand the square:**
$$\left(2 - \frac{1}{2}x\right)^2 = 4 - 2x + \frac{1}{4}x^2$$
6. **Integral becomes:**
$$V = \pi \int_1^2 \left(4 - 2x + \frac{1}{4}x^2\right) dx$$
7. **Integrate term-by-term:**
$$\int_1^2 4 \, dx = 4x \Big|_1^2 = 4(2) - 4(1) = 8 - 4 = 4$$
$$\int_1^2 (-2x) \, dx = -2 \cdot \frac{x^2}{2} \Big|_1^2 = -x^2 \Big|_1^2 = -(4 - 1) = -3$$
$$\int_1^2 \frac{1}{4}x^2 \, dx = \frac{1}{4} \cdot \frac{x^3}{3} \Big|_1^2 = \frac{1}{12}(8 - 1) = \frac{7}{12}$$
8. **Sum the integrals:**
$$4 - 3 + \frac{7}{12} = 1 + \frac{7}{12} = \frac{12}{12} + \frac{7}{12} = \frac{19}{12}$$
9. **Multiply by $\pi$:**
$$V = \pi \cdot \frac{19}{12} = \frac{19\pi}{12}$$
**Final answer:**
$$\boxed{\frac{19\pi}{12}}$$
This is the volume of the solid formed by rotating the given region about the x-axis.