Intervals Fx 1
1. We are given the function $f(x) = x^2 - 3x + 8$ and need to find:
(a) intervals where $f$ is increasing,
(b) intervals where $f$ is decreasing,
(c) intervals where $f$ is concave up,
(d) intervals where $f$ is concave down,
(e) $x$-coordinates of inflection points.
2. To analyze increasing/decreasing behavior, use the first derivative test:
$$f'(x) = \frac{d}{dx}(x^2 - 3x + 8) = 2x - 3$$
3. To analyze concavity and inflection points, use the second derivative:
$$f''(x) = \frac{d}{dx}(2x - 3) = 2$$
4. Find critical points by setting $f'(x) = 0$:
$$2x - 3 = 0 \implies x = \frac{3}{2}$$
5. Determine intervals of increase/decrease:
- For $x < \frac{3}{2}$, $f'(x) = 2x - 3 < 0$ so $f$ is decreasing.
- For $x > \frac{3}{2}$, $f'(x) = 2x - 3 > 0$ so $f$ is increasing.
6. Since $f''(x) = 2 > 0$ for all $x$, $f$ is concave up everywhere.
7. Because $f''(x)$ never changes sign, there are no inflection points.
Final answers:
(a) Increasing on $(\frac{3}{2}, \infty)$
(b) Decreasing on $(-\infty, \frac{3}{2})$
(c) Concave up on $(-\infty, \infty)$
(d) Concave down on $\varnothing$ (no intervals)
(e) No inflection points