Extreme Values 42Aef1
1. **State the problem:** Find the extreme values of the function $f(x) = x^3 - 18x^2 + 96$ using the second derivative test.
2. **Recall the formulas and rules:**
- The first derivative $f'(x)$ gives critical points where $f'(x) = 0$.
- The second derivative $f''(x)$ helps classify these points:
- If $f''(x) > 0$, the point is a local minimum.
- If $f''(x) < 0$, the point is a local maximum.
- If $f''(x) = 0$, the test is inconclusive.
3. **Find the first derivative:**
$$f'(x) = \frac{d}{dx}(x^3 - 18x^2 + 96) = 3x^2 - 36x$$
4. **Find critical points by solving $f'(x) = 0$:**
$$3x^2 - 36x = 0$$
$$3x(x - 12) = 0$$
So, $x = 0$ or $x = 12$ are critical points.
5. **Find the second derivative:**
$$f''(x) = \frac{d}{dx}(3x^2 - 36x) = 6x - 36$$
6. **Evaluate $f''(x)$ at critical points:**
- At $x=0$: $f''(0) = 6(0) - 36 = -36 < 0$, so $x=0$ is a local maximum.
- At $x=12$: $f''(12) = 6(12) - 36 = 72 - 36 = 36 > 0$, so $x=12$ is a local minimum.
7. **Find the extreme values by plugging back into $f(x)$:**
- $f(0) = 0^3 - 18(0)^2 + 96 = 96$
- $f(12) = 12^3 - 18(12)^2 + 96 = 1728 - 2592 + 96 = -768$
**Final answer:**
- Local maximum at $x=0$ with value $96$.
- Local minimum at $x=12$ with value $-768$.