Maxima Minima 1D39Ea
1. **State the problem:** Find the local and absolute maxima and minima of the function $$f(x) = 3x - 6 \cos(x)$$ on the interval $$[-\pi, \pi]$$.
2. **Find the derivative:** To find critical points, compute $$f'(x)$$:
$$f'(x) = 3 - 6(-\sin(x)) = 3 + 6\sin(x)$$.
3. **Set derivative to zero to find critical points:**
$$3 + 6\sin(x) = 0 \implies \sin(x) = -\frac{1}{2}$$.
4. **Solve for $$x$$ in $$[-\pi, \pi]$$ where $$\sin(x) = -\frac{1}{2}$$:**
The solutions are $$x = -\frac{\pi}{6}$$ and $$x = -\frac{5\pi}{6}$$.
5. **Determine the nature of critical points using the second derivative:**
$$f''(x) = 6\cos(x)$$.
Evaluate at critical points:
- At $$x = -\frac{\pi}{6}$$, $$f''\left(-\frac{\pi}{6}\right) = 6\cos\left(-\frac{\pi}{6}\right) = 6 \times \frac{\sqrt{3}}{2} = 3\sqrt{3} > 0$$, so local minimum.
- At $$x = -\frac{5\pi}{6}$$, $$f''\left(-\frac{5\pi}{6}\right) = 6\cos\left(-\frac{5\pi}{6}\right) = 6 \times \left(-\frac{\sqrt{3}}{2}\right) = -3\sqrt{3} < 0$$, so local maximum.
6. **Evaluate $$f(x)$$ at critical points and endpoints to find absolute extrema:**
- $$f\left(-\frac{\pi}{6}\right) = 3\left(-\frac{\pi}{6}\right) - 6\cos\left(-\frac{\pi}{6}\right) = -\frac{\pi}{2} - 6 \times \frac{\sqrt{3}}{2} = -\frac{\pi}{2} - 3\sqrt{3}$$
- $$f\left(-\frac{5\pi}{6}\right) = 3\left(-\frac{5\pi}{6}\right) - 6\cos\left(-\frac{5\pi}{6}\right) = -\frac{5\pi}{2} - 6 \times \left(-\frac{\sqrt{3}}{2}\right) = -\frac{5\pi}{2} + 3\sqrt{3}$$
- $$f(-\pi) = 3(-\pi) - 6\cos(-\pi) = -3\pi - 6(-1) = -3\pi + 6$$
- $$f(\pi) = 3\pi - 6\cos(\pi) = 3\pi - 6(-1) = 3\pi + 6$$
7. **Compare values:**
- $$f(-\pi) = -3\pi + 6 \approx -9.424 + 6 = -3.424$$
- $$f\left(-\frac{5\pi}{6}\right) \approx -\frac{5 \times 3.1416}{2} + 3 \times 1.732 = -7.854 + 5.196 = -2.658$$
- $$f\left(-\frac{\pi}{6}\right) \approx -\frac{3.1416}{2} - 3 \times 1.732 = -1.571 - 5.196 = -6.767$$
- $$f(\pi) = 3\pi + 6 \approx 9.424 + 6 = 15.424$$
8. **Conclusions:**
- Local maxima at $$x = -\frac{5\pi}{6}$$ with value $$f\left(-\frac{5\pi}{6}\right)$$.
- Local minima at $$x = -\frac{\pi}{6}$$ with value $$f\left(-\frac{\pi}{6}\right)$$.
- Absolute maximum at $$x = \pi$$ with value $$f(\pi)$$.
- Absolute minimum at $$x = -\frac{\pi}{6}$$ with value $$f\left(-\frac{\pi}{6}\right)$$.
**Final answers:**
- Local maxima: $$-\frac{5\pi}{6}$$
- Local minima: $$-\frac{\pi}{6}$$
- Absolute maxima: $$\pi$$
- Absolute minima: $$-\frac{\pi}{6}$$