Area Enclosed Dbe745
1. **State the problem:**
We need to find the area of the region enclosed by the curves $y=\sec^2 x$ and $y=8\cos x$ over the interval $-\frac{\pi}{3} \le x \le \frac{\pi}{3}$.
2. **Understand the curves and interval:**
- $y=\sec^2 x = \frac{1}{\cos^2 x}$ is always positive and increases as $x$ approaches $\pm \frac{\pi}{2}$.
- $y=8\cos x$ oscillates between $8$ and $-8$.
- The interval is symmetric about zero.
3. **Find points of intersection:**
Set $\sec^2 x = 8 \cos x$:
$$\frac{1}{\cos^2 x} = 8 \cos x \implies 1 = 8 \cos^3 x \implies \cos^3 x = \frac{1}{8} \implies \cos x = \frac{1}{2}.$$
4. **Solve for $x$:**
$$\cos x = \frac{1}{2} \implies x = \pm \frac{\pi}{3}$$
These are the endpoints of the interval, so the curves intersect at the boundaries.
5. **Determine which curve is on top between $-\frac{\pi}{3}$ and $\frac{\pi}{3}$:**
At $x=0$:
$$y=\sec^2 0 = 1, \quad y=8 \cos 0 = 8,$$
so $8 \cos x$ is above $\sec^2 x$ in the interval.
6. **Set up the integral for the area:**
The area $A$ is
$$A = \int_{-\frac{\pi}{3}}^{\frac{\pi}{3}} \left(8 \cos x - \sec^2 x\right) dx.$$
7. **Calculate the integral:**
$$\int 8 \cos x \, dx = 8 \sin x,$$
$$\int \sec^2 x \, dx = \tan x.$$
8. **Evaluate definite integral:**
$$A = \left[8 \sin x - \tan x \right]_{-\frac{\pi}{3}}^{\frac{\pi}{3}} = \left(8 \sin \frac{\pi}{3} - \tan \frac{\pi}{3}\right) - \left(8 \sin \left(-\frac{\pi}{3}\right) - \tan \left(-\frac{\pi}{3}\right)\right).$$
9. **Use exact values:**
$$\sin \frac{\pi}{3} = \frac{\sqrt{3}}{2}, \quad \tan \frac{\pi}{3} = \sqrt{3}.$$
10. **Substitute:**
$$A = \left(8 \cdot \frac{\sqrt{3}}{2} - \sqrt{3}\right) - \left(8 \cdot \left(-\frac{\sqrt{3}}{2}\right) - (-\sqrt{3})\right) = \left(4 \sqrt{3} - \sqrt{3}\right) - \left(-4 \sqrt{3} + \sqrt{3}\right).$$
11. **Simplify:**
$$= (3 \sqrt{3}) - (-3 \sqrt{3}) = 3 \sqrt{3} + 3 \sqrt{3} = 6 \sqrt{3}.$$