Rational Inequalities
1. Solve $$\frac{2x}{x+6} \geq 1$$
Step 1: Move all terms to one side:
$$\frac{2x}{x+6} - 1 \geq 0$$
Step 2: Write with common denominator:
$$\frac{2x - (x+6)}{x+6} \geq 0\implies \frac{2x - x - 6}{x+6} \geq 0$$
Simplify numerator:
$$\frac{x - 6}{x+6} \geq 0$$
Step 3: Determine critical points where numerator or denominator are zero:
Numerator zero at $$x=6$$
Denominator zero at $$x=-6$$ (excluded from domain)
Step 4: Test intervals divided by $$-6$$ and $$6$$:
- For $$x < -6$$, denominator negative, numerator negative, fraction positive
- For $$-6 < x < 6$$, denominator positive, numerator negative, fraction negative
- For $$x > 6$$, denominator positive, numerator positive, fraction positive
Step 5: Combine intervals where fraction $$\geq 0$$:
$$(-\infty, -6) \cup [6, \infty)$$ with $$x \neq -6$$ (excluded)
2. Solve $$\frac{x+4}{x+3} \geq 0$$
Step 1: Critical points where numerator/denominator zero:
Numerator zero at $$x = -4$$
Denominator zero at $$x = -3$$ (excluded)
Step 2: Test intervals:
- For $$x < -4$$, numerator negative, denominator negative, fraction positive
- For $$-4 < x < -3$$, numerator positive, denominator negative, fraction negative
- For $$x > -3$$, numerator positive, denominator positive, fraction positive
Step 3: Combine intervals where fraction $$\geq 0$$:
$$(-\infty, -4] \cup (-3, \infty)$$
3. Solve $$\frac{x^2 - x - 12}{x+2} \geq 0$$
Step 1: Factor numerator:
$$x^2 - x - 12 = (x - 4)(x + 3)$$
Step 2: Critical points: numerator zero at $$x=4, -3$$; denominator zero at $$x=-2$$ (excluded)
Step 3: Write expression:
$$\frac{(x-4)(x+3)}{x+2} \geq 0$$
Step 4: Test intervals divided by $$-3, -2, 4$$:
- $$x < -3$$: numerator positive (since both factors negative times negative = positive), denominator negative, fraction negative
- $$-3 < x < -2$$: numerator negative, denominator negative, fraction positive
- $$-2 < x < 4$$: numerator negative, denominator positive, fraction negative
- $$x > 4$$: numerator positive, denominator positive, fraction positive
Step 5: Include points where numerator zero and denominator not zero:
$$x=-3, 4$$ included
Answer:
$$[-3, -2) \cup [4, \infty)$$
4. Solve $$\frac{x^2 -16}{x^2 -1} \leq 0$$
Step 1: Factor numerator and denominator:
Numerator: $$x^2 -16 = (x-4)(x+4)$$
Denominator: $$x^2 -1 = (x-1)(x+1)$$
Step 2: Critical points:
Numerator zero at $$-4, 4$$
Denominator zero at $$-1, 1$$ (excluded)
Step 3: Expression:
$$\frac{(x-4)(x+4)}{(x-1)(x+1)} \leq 0$$
Step 4: Intervals divided by $$-4, -1, 1, 4$$
- $$x < -4$$: Numerator positive, denominator positive, fraction positive
- $$-4 < x < -1$$: Numerator negative, denominator positive, fraction negative
- $$-1 < x < 1$$: Numerator negative, denominator negative, fraction positive
- $$1 < x < 4$$: Numerator positive, denominator negative, fraction negative
- $$x > 4$$: Numerator positive, denominator positive, fraction positive
Step 5: Combine intervals where fraction $$\leq 0$$ plus zeros of numerator:
$$(-4, -1) \cup (1,4)$$ with $$x \neq -1, 1$$
Include points where numerator zero: $$-4, 4$$ included
Answer:
$$[-4, -1) \cup (1, 4]$$
5. Solve $$\frac{x+2}{x-4} \leq 1$$
Step 1: Move right side:
$$\frac{x+2}{x-4} - 1 \leq 0$$
Step 2: Common denominator:
$$\frac{x+2 - (x-4)}{x-4} \leq 0 \implies \frac{x+2 - x + 4}{x-4} \leq 0$$
Simplify numerator:
$$\frac{6}{x-4} \leq 0$$
Step 3: Analyze fraction:
Numerator is positive constant 6
Fraction $$\leq 0$$ when denominator negative:
$$x-4 < 0 \Rightarrow x < 4$$
Step 4: Final solution:
$$(-\infty, 4)$$ with $$x \neq 4$$ (domain restriction)
Final answers:
1. $$(-\infty, -6) \cup [6, \infty)$$
2. $$(-\infty, -4] \cup (-3, \infty)$$
3. $$[-3, -2) \cup [4, \infty)$$
4. $$[-4, -1) \cup (1, 4]$$
5. $$(-\infty, 4)$$