1. **Problem Statement:**
Find the volume of the solid generated by rotating the region bounded by the curves $y = x^2$ and $y = x + 2$ about the $y$-axis through 360°.
2. **Identify the curves and limits:**
Given curves:
$$y = x^2$$
$$y = x + 2$$
Find intersection points by setting $x^2 = x + 2$:
$$x^2 - x - 2 = 0$$
Factor:
$$(x - 2)(x + 1) = 0$$
So, $x = 2$ and $x = -1$.
Corresponding $y$ values:
$$y_1 = (2)^2 = 4$$
$$y_2 = (-1)^2 = 1$$
So the limits for $y$ are from 1 to 4.
3. **Express $x$ as functions of $y$ for rotation about $y$-axis:**
From $y = x^2$, we get:
$$x = \sqrt{y}$$
From $y = x + 2$, solve for $x$:
$$x = y - 2$$
4. **Volume formula for rotation about $y$-axis:**
$$V = \pi \int_{c}^{d} \left[ R(y)^2 - r(y)^2 \right] dy$$
where $R(y)$ is the outer radius and $r(y)$ is the inner radius.
5. **Determine outer and inner radius:**
Since $x = \sqrt{y}$ is to the right of $x = y - 2$ in the interval $y \in [1,4]$, outer radius is $\sqrt{y}$ and inner radius is $y - 2$.
6. **Set up the integral:**
$$V = \pi \int_1^4 \left( (\sqrt{y})^2 - (y - 2)^2 \right) dy = \pi \int_1^4 \left( y - (y^2 - 4y + 4) \right) dy$$
7. **Simplify the integrand:**
$$y - y^2 + 4y - 4 = -y^2 + 5y - 4$$
8. **Integrate:**
$$V = \pi \int_1^4 (-y^2 + 5y - 4) dy = \pi \left[ -\frac{y^3}{3} + \frac{5y^2}{2} - 4y \right]_1^4$$
9. **Evaluate the definite integral:**
Calculate at upper limit $y=4$:
$$-\frac{4^3}{3} + \frac{5 \cdot 4^2}{2} - 4 \cdot 4 = -\frac{64}{3} + \frac{80}{2} - 16 = -\frac{64}{3} + 40 - 16 = -\frac{64}{3} + 24$$
Calculate at lower limit $y=1$:
$$-\frac{1^3}{3} + \frac{5 \cdot 1^2}{2} - 4 \cdot 1 = -\frac{1}{3} + \frac{5}{2} - 4 = -\frac{1}{3} + 2.5 - 4 = -\frac{1}{3} - 1.5 = -\frac{1}{3} - \frac{3}{2} = -\frac{11}{6}$$
Subtract lower from upper:
$$\left(-\frac{64}{3} + 24\right) - \left(-\frac{11}{6}\right) = -\frac{64}{3} + 24 + \frac{11}{6}$$
Find common denominator 6:
$$-\frac{128}{6} + \frac{144}{6} + \frac{11}{6} = \frac{27}{6} = \frac{9}{2}$$
10. **Final volume:**
$$V = \pi \times \frac{9}{2} = \frac{9\pi}{2}$$
**Answer:** The volume of the solid is $\boxed{\frac{9\pi}{2}}$ cubic units.
Volume Benda Putar Y Axis 32Ddfb
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