Extreme Values A38853
1. **State the problem:** Find the extreme values of the function $f(x) = x^3 - 18x^2 + 96$ using the second derivative test.
2. **Find the first derivative:**
$$f'(x) = \frac{d}{dx}(x^3 - 18x^2 + 96) = 3x^2 - 36x$$
3. **Find critical points by setting $f'(x) = 0$:**
$$3x^2 - 36x = 0$$
$$3x(x - 12) = 0$$
Critical points are $x = 0$ and $x = 12$.
4. **Find the second derivative:**
$$f''(x) = \frac{d}{dx}(3x^2 - 36x) = 6x - 36$$
5. **Apply the second derivative test:**
- At $x=0$:
$$f''(0) = 6(0) - 36 = -36 < 0$$
Since $f''(0) < 0$, $f$ has a local maximum at $x=0$.
- At $x=12$:
$$f''(12) = 6(12) - 36 = 72 - 36 = 36 > 0$$
Since $f''(12) > 0$, $f$ has a local minimum at $x=12$.
6. **Find the extreme values by evaluating $f(x)$ at critical points:**
- $f(0) = 0^3 - 18(0)^2 + 96 = 96$
- $f(12) = 12^3 - 18(12)^2 + 96 = 1728 - 2592 + 96 = -768$
**Final answer:**
- Local maximum value is $96$ at $x=0$.
- Local minimum value is $-768$ at $x=12$.