1. **State the problem:** Solve the inequality $$\frac{1}{x} + \frac{1}{x+1} > \frac{3}{2}$$ for $x$.
2. **Find a common denominator and combine the left side:** The common denominator is $x(x+1)$.
$$\frac{1}{x} + \frac{1}{x+1} = \frac{x+1}{x(x+1)} + \frac{x}{x(x+1)} = \frac{x+1+x}{x(x+1)} = \frac{2x+1}{x(x+1)}$$
3. **Rewrite the inequality:**
$$\frac{2x+1}{x(x+1)} > \frac{3}{2}$$
4. **Bring all terms to one side:**
$$\frac{2x+1}{x(x+1)} - \frac{3}{2} > 0$$
5. **Find a common denominator for the entire expression:**
$$\frac{2(2x+1)}{2x(x+1)} - \frac{3x(x+1)}{2x(x+1)} > 0$$
6. **Combine the fractions:**
$$\frac{2(2x+1) - 3x(x+1)}{2x(x+1)} > 0$$
7. **Expand numerator:**
$$2(2x+1) = 4x + 2$$
$$3x(x+1) = 3x^2 + 3x$$
8. **Substitute back:**
$$\frac{4x + 2 - (3x^2 + 3x)}{2x(x+1)} > 0$$
9. **Simplify numerator:**
$$4x + 2 - 3x^2 - 3x = -3x^2 + x + 2$$
10. **Rewrite inequality:**
$$\frac{-3x^2 + x + 2}{2x(x+1)} > 0$$
11. **Factor numerator:**
$$-3x^2 + x + 2 = -(3x^2 - x - 2)$$
12. **Factor quadratic inside parentheses:**
$$3x^2 - x - 2 = (3x + 2)(x - 1)$$
13. **Rewrite numerator:**
$$-(3x + 2)(x - 1)$$
14. **Rewrite entire inequality:**
$$\frac{-(3x + 2)(x - 1)}{2x(x+1)} > 0$$
15. **Analyze critical points:** The expression is undefined or zero at $x = -1, 0, -\frac{2}{3}, 1$.
16. **Determine sign intervals:** Test values in intervals divided by these points:
- $(-\infty, -1)$
- $(-1, -\frac{2}{3})$
- $(-\frac{2}{3}, 0)$
- $(0, 1)$
- $(1, \infty)$
17. **Sign analysis:**
- For $x < -1$, numerator negative (since $-(3x+2)(x-1)$), denominator positive (since $2x(x+1)$ with both factors negative, product positive), fraction negative.
- For $-1 < x < -\frac{2}{3}$, numerator positive, denominator negative, fraction negative.
- For $-\frac{2}{3} < x < 0$, numerator negative, denominator negative, fraction positive.
- For $0 < x < 1$, numerator negative, denominator positive, fraction negative.
- For $x > 1$, numerator positive, denominator positive, fraction positive.
18. **Solution set:** Inequality holds where fraction $> 0$, so
$$x \in \left(-\frac{2}{3}, 0\right) \cup (1, \infty)$$
19. **Exclude points where denominator is zero:** $x \neq -1, 0$.
**Final answer:**
$$\boxed{\left(-\frac{2}{3}, 0\right) \cup (1, \infty)}$$
Fraction Inequality 1698A2
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