Area Volume Enclosed
1. **Problem 1: Find the area enclosed by the curves** $y = x^2$ and $y^2 = 8x$.
2. First, rewrite $y^2 = 8x$ as $y = \pm \sqrt{8x} = \pm 2\sqrt{2x}$.
3. Find the points of intersection by setting $y = x^2$ equal to $y = 2\sqrt{2x}$ (considering the positive branch since $x^2 \geq 0$):
$$x^2 = 2\sqrt{2x}$$
4. Square both sides:
$$x^4 = 4 \cdot 2x = 8x$$
5. Rearrange:
$$x^4 - 8x = 0$$
6. Factor:
$$x(x^3 - 8) = 0$$
7. Solutions:
$$x = 0 \quad \text{or} \quad x^3 = 8 \Rightarrow x = 2$$
8. The curves intersect at $x=0$ and $x=2$.
9. The area enclosed is between $x=0$ and $x=2$, bounded by $y=2\sqrt{2x}$ (upper curve) and $y=x^2$ (lower curve).
10. Area $A$ is:
$$A = \int_0^2 \left(2\sqrt{2x} - x^2\right) dx$$
11. Simplify the integrand:
$$2\sqrt{2x} = 2 \cdot \sqrt{2} \cdot \sqrt{x} = 2\sqrt{2} x^{1/2}$$
12. Compute the integral:
$$A = \int_0^2 \left(2\sqrt{2} x^{1/2} - x^2\right) dx = 2\sqrt{2} \int_0^2 x^{1/2} dx - \int_0^2 x^2 dx$$
13. Evaluate each integral:
$$\int_0^2 x^{1/2} dx = \left[ \frac{2}{3} x^{3/2} \right]_0^2 = \frac{2}{3} (2)^{3/2} = \frac{2}{3} \cdot 2^{1.5} = \frac{2}{3} \cdot 2 \sqrt{2} = \frac{4 \sqrt{2}}{3}$$
$$\int_0^2 x^2 dx = \left[ \frac{x^3}{3} \right]_0^2 = \frac{8}{3}$$
14. Substitute back:
$$A = 2\sqrt{2} \cdot \frac{4 \sqrt{2}}{3} - \frac{8}{3} = \frac{8 \cdot 2}{3} - \frac{8}{3} = \frac{16}{3} - \frac{8}{3} = \frac{8}{3}$$
15. **Area enclosed by the curves is** $\boxed{\frac{8}{3}}$.
---
16. **Problem 2: Find the volume of the solid formed by rotating the area between the curves about the x-axis.**
17. The volume $V$ is given by the washer method:
$$V = \pi \int_0^2 \left( (2\sqrt{2x})^2 - (x^2)^2 \right) dx$$
18. Simplify the integrand:
$$(2\sqrt{2x})^2 = 4 \cdot 2x = 8x$$
$$(x^2)^2 = x^4$$
19. So,
$$V = \pi \int_0^2 (8x - x^4) dx$$
20. Compute the integral:
$$\int_0^2 8x dx = \left[4x^2\right]_0^2 = 4 \cdot 4 = 16$$
$$\int_0^2 x^4 dx = \left[ \frac{x^5}{5} \right]_0^2 = \frac{32}{5}$$
21. Substitute back:
$$V = \pi (16 - \frac{32}{5}) = \pi \left( \frac{80}{5} - \frac{32}{5} \right) = \pi \cdot \frac{48}{5} = \frac{48\pi}{5}$$
22. **Volume of the solid of revolution is** $\boxed{\frac{48\pi}{5}}$.
---
23. **Problem 3: Find the area enclosed between the curves** $y = x^2$ and $y = 4 - x^2$.
24. Find points of intersection by setting:
$$x^2 = 4 - x^2$$
25. Rearrange:
$$2x^2 = 4 \Rightarrow x^2 = 2 \Rightarrow x = \pm \sqrt{2}$$
26. The curves intersect at $x = -\sqrt{2}$ and $x = \sqrt{2}$.
27. The upper curve is $y = 4 - x^2$ and the lower curve is $y = x^2$.
28. Area $A$ is:
$$A = \int_{-\sqrt{2}}^{\sqrt{2}} \left(4 - x^2 - x^2\right) dx = \int_{-\sqrt{2}}^{\sqrt{2}} (4 - 2x^2) dx$$
29. Compute the integral:
$$\int (4 - 2x^2) dx = 4x - \frac{2x^3}{3}$$
30. Evaluate from $-\sqrt{2}$ to $\sqrt{2}$:
$$A = \left[4x - \frac{2x^3}{3}\right]_{-\sqrt{2}}^{\sqrt{2}} = \left(4\sqrt{2} - \frac{2(\sqrt{2})^3}{3}\right) - \left(-4\sqrt{2} + \frac{2(-\sqrt{2})^3}{3}\right)$$
31. Simplify powers:
$$(\sqrt{2})^3 = (2^{1/2})^3 = 2^{3/2} = 2 \sqrt{2}$$
32. Substitute:
$$= \left(4\sqrt{2} - \frac{2 \cdot 2 \sqrt{2}}{3}\right) - \left(-4\sqrt{2} + \frac{2 \cdot (-2 \sqrt{2})}{3}\right)$$
$$= \left(4\sqrt{2} - \frac{4 \sqrt{2}}{3}\right) - \left(-4\sqrt{2} - \frac{4 \sqrt{2}}{3}\right)$$
33. Simplify inside parentheses:
$$= \left(\frac{12\sqrt{2}}{3} - \frac{4\sqrt{2}}{3}\right) - \left(-\frac{12\sqrt{2}}{3} - \frac{4\sqrt{2}}{3}\right) = \frac{8\sqrt{2}}{3} - \left(-\frac{16\sqrt{2}}{3}\right) = \frac{8\sqrt{2}}{3} + \frac{16\sqrt{2}}{3} = \frac{24\sqrt{2}}{3} = 8\sqrt{2}$$
34. **Area enclosed between the curves is** $\boxed{8\sqrt{2}}$.