Increasing Decreasing Extrema
1. **State the problem:** We have the function $$f(x) = 2x^3 - 12x^2 + 18x - 8$$ and need to find where it is increasing, decreasing, and its local extrema.
2. **Find the derivative:** To analyze increasing/decreasing intervals and local extrema, compute $$f'(x)$$:
$$f'(x) = \frac{d}{dx}(2x^3 - 12x^2 + 18x - 8) = 6x^2 - 24x + 18$$
3. **Find critical points:** Set $$f'(x) = 0$$:
$$6x^2 - 24x + 18 = 0$$
Divide both sides by 6:
$$x^2 - 4x + 3 = 0$$
Factor:
$$(x - 3)(x - 1) = 0$$
So critical points are at $$x = 1$$ and $$x = 3$$.
4. **Determine intervals of increase/decrease:** Test values in intervals determined by critical points:
- For $$x < 1$$, pick $$x=0$$:
$$f'(0) = 6(0)^2 - 24(0) + 18 = 18 > 0$$, so $$f$$ is increasing on $$(-\infty, 1)$$.
- For $$1 < x < 3$$, pick $$x=2$$:
$$f'(2) = 6(4) - 24(2) + 18 = 24 - 48 + 18 = -6 < 0$$, so $$f$$ is decreasing on $$(1, 3)$$.
- For $$x > 3$$, pick $$x=4$$:
$$f'(4) = 6(16) - 24(4) + 18 = 96 - 96 + 18 = 18 > 0$$, so $$f$$ is increasing on $$(3, \infty)$$.
5. **Find local extrema values:** Evaluate $$f(x)$$ at critical points:
- At $$x=1$$:
$$f(1) = 2(1)^3 - 12(1)^2 + 18(1) - 8 = 2 - 12 + 18 - 8 = 0$$
- At $$x=3$$:
$$f(3) = 2(27) - 12(9) + 18(3) - 8 = 54 - 108 + 54 - 8 = -8$$
6. **Classify extrema:** Since $$f'$$ changes from positive to negative at $$x=1$$, $$f(1)=0$$ is a local maximum.
Since $$f'$$ changes from negative to positive at $$x=3$$, $$f(3)=-8$$ is a local minimum.
**Final answers:**
(a) Increasing on $$(-\infty, 1) \cup (3, \infty)$$
(b) Decreasing on $$(1, 3)$$
(c) Local maximum value: $$0$$ at $$x=1$$
Local minimum value: $$-8$$ at $$x=3$$