Function Analysis A78D5A
1. **Stating the problem:** We are given the function $$f(x) = 2x + \ln(x^2 - 3)$$ and asked to analyze it by finding:
a) The domain of $$f$$
b) Intervals where $$f$$ is increasing or decreasing
c) Relative/local extrema
d) Intervals where $$f$$ is concave up or concave down
e) Points of inflection
f) Asymptotes
2. **Domain of $$f$$:** The function contains $$\ln(x^2 - 3)$$, so the argument must be positive:
$$x^2 - 3 > 0 \implies x^2 > 3 \implies x < -\sqrt{3} \text{ or } x > \sqrt{3}$$
Therefore, the domain is $$(-\infty, -\sqrt{3}) \cup (\sqrt{3}, \infty)$$.
3. **First derivative $$f'(x)$$ to find increasing/decreasing intervals:**
$$f'(x) = \frac{d}{dx} \left(2x + \ln(x^2 - 3)\right) = 2 + \frac{1}{x^2 - 3} \cdot 2x = 2 + \frac{2x}{x^2 - 3}$$
Simplify:
$$f'(x) = 2 + \frac{2x}{x^2 - 3} = \frac{2(x^2 - 3)}{x^2 - 3} + \frac{2x}{x^2 - 3} = \frac{2x^2 - 6 + 2x}{x^2 - 3} = \frac{2x^2 + 2x - 6}{x^2 - 3}$$
4. **Critical points:** Set numerator equal to zero:
$$2x^2 + 2x - 6 = 0 \implies x^2 + x - 3 = 0$$
Solve using quadratic formula:
$$x = \frac{-1 \pm \sqrt{1 + 12}}{2} = \frac{-1 \pm \sqrt{13}}{2}$$
Both roots are in the domain since $$\sqrt{13} \approx 3.6$$, so:
$$x_1 = \frac{-1 - 3.6}{2} = -2.3$$ (in $$(-\infty, -\sqrt{3})$$)
$$x_2 = \frac{-1 + 3.6}{2} = 1.3$$ (in $$(\sqrt{3}, \infty)$$)
5. **Sign analysis of $$f'(x)$$:**
Denominator $$x^2 - 3 > 0$$ in domain, so sign depends on numerator:
- For $$x < -2.3$$, numerator $$> 0$$ (test $$x = -3$$: $$2(9) + 2(-3) - 6 = 18 - 6 - 6 = 6 > 0$$)
- For $$-2.3 < x < -\sqrt{3}$$, numerator $$< 0$$ (test $$x = -1.8$$: $$2(3.24) + 2(-1.8) - 6 = 6.48 - 3.6 - 6 = -3.12 < 0$$)
- For $$x > 1.3$$, numerator $$> 0$$ (test $$x=2$$: $$8 + 4 - 6 = 6 > 0$$)
So:
- Increasing on $$(-\infty, -2.3) \cup (1.3, \infty)$$
- Decreasing on $$(-2.3, -\sqrt{3}) \cup (\sqrt{3}, 1.3)$$
6. **Relative extrema:**
- At $$x = -2.3$$, $$f'$$ changes from positive to negative, so local maximum.
- At $$x = 1.3$$, $$f'$$ changes from negative to positive, so local minimum.
7. **Second derivative $$f''(x)$$ for concavity:**
$$f''(x) = \frac{d}{dx} f'(x) = \frac{d}{dx} \left(2 + \frac{2x}{x^2 - 3}\right) = \frac{d}{dx} \left(\frac{2x}{x^2 - 3}\right)$$
Use quotient rule:
$$f''(x) = \frac{(2)(x^2 - 3) - 2x(2x)}{(x^2 - 3)^2} = \frac{2x^2 - 6 - 4x^2}{(x^2 - 3)^2} = \frac{-2x^2 - 6}{(x^2 - 3)^2}$$
8. **Concavity intervals:**
Numerator $$-2x^2 - 6 < 0$$ for all real $$x$$.
Denominator $$> 0$$ in domain.
So $$f''(x) < 0$$ everywhere in domain, meaning $$f$$ is concave down on $$(-\infty, -\sqrt{3}) \cup (\sqrt{3}, \infty)$$.
9. **Points of inflection:** Since $$f''(x)$$ does not change sign in domain, no points of inflection.
10. **Asymptotes:**
- Vertical asymptotes at points where denominator of $$\ln$$ argument is zero or undefined: at $$x = \pm \sqrt{3}$$.
- Horizontal or oblique asymptotes: As $$x \to \pm \infty$$,
$$f(x) \approx 2x + \ln(x^2) = 2x + 2\ln|x|$$ which grows without bound, so no horizontal asymptotes.
**Final answers:**
- Domain: $$(-\infty, -\sqrt{3}) \cup (\sqrt{3}, \infty)$$
- Increasing on $$(-\infty, -2.3) \cup (1.3, \infty)$$
- Decreasing on $$(-2.3, -\sqrt{3}) \cup (\sqrt{3}, 1.3)$$
- Local max at $$x = \frac{-1 - \sqrt{13}}{2} \approx -2.3$$
- Local min at $$x = \frac{-1 + \sqrt{13}}{2} \approx 1.3$$
- Concave down everywhere in domain
- No inflection points
- Vertical asymptotes at $$x = \pm \sqrt{3}$$