Local Extrema 20D7B7
1. **State the problem:** We need to find the local maxima and minima of the function $$f(x)=x^3-6x^2+9x+1$$ using the second derivative test.
2. **Find the first derivative:** The first derivative $$f'(x)$$ gives the slope of the function and helps find critical points.
$$f'(x) = \frac{d}{dx}(x^3-6x^2+9x+1) = 3x^2 - 12x + 9$$
3. **Find critical points:** Set $$f'(x) = 0$$ to find critical points.
$$3x^2 - 12x + 9 = 0$$
Divide both sides by 3:
$$x^2 - 4x + 3 = 0$$
Factor:
$$(x-3)(x-1) = 0$$
So, critical points are $$x=1$$ and $$x=3$$.
4. **Find the second derivative:**
$$f''(x) = \frac{d}{dx}(3x^2 - 12x + 9) = 6x - 12$$
5. **Apply the second derivative test:**
- At $$x=1$$:
$$f''(1) = 6(1) - 12 = 6 - 12 = -6 < 0$$, so $$f$$ has a local maximum at $$x=1$$.
- At $$x=3$$:
$$f''(3) = 6(3) - 12 = 18 - 12 = 6 > 0$$, so $$f$$ has a local minimum at $$x=3$$.
6. **Find the function values at critical points:**
- $$f(1) = 1^3 - 6(1)^2 + 9(1) + 1 = 1 - 6 + 9 + 1 = 5$$
- $$f(3) = 3^3 - 6(3)^2 + 9(3) + 1 = 27 - 54 + 27 + 1 = 1$$
**Final answer:**
- Local maximum at $$x=1$$ with value $$f(1)=5$$.
- Local minimum at $$x=3$$ with value $$f(3)=1$$.