Wyatt Huang
04/13/2023 · Primary School
Solve the inequality \( \frac{9}{x+1} \geq-5 \). Use exact values when entering the answer.
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Step-by-step Solution
To solve the inequality \( \frac{9}{x+1} \geq -5 \), we start by isolating the fraction. We can rewrite the inequality as:
\[
\frac{9}{x+1} + 5 \geq 0
\]
To combine the terms, we need a common denominator. The common denominator is \( x + 1 \):
\[
\frac{9}{x+1} + \frac{5(x+1)}{x+1} \geq 0
\]
This simplifies to:
\[
\frac{9 + 5(x + 1)}{x + 1} \geq 0
\]
Expanding the numerator:
\[
\frac{9 + 5x + 5}{x + 1} \geq 0
\]
This simplifies to:
\[
\frac{5x + 14}{x + 1} \geq 0
\]
Next, we need to find the critical points where the expression is equal to zero or undefined. The numerator \( 5x + 14 = 0 \) gives:
\[
5x + 14 = 0 \implies 5x = -14 \implies x = -\frac{14}{5}
\]
The denominator \( x + 1 = 0 \) gives:
\[
x + 1 = 0 \implies x = -1
\]
Now we have two critical points: \( x = -\frac{14}{5} \) and \( x = -1 \). We will test the intervals determined by these points:
1. \( (-\infty, -\frac{14}{5}) \)
2. \( (-\frac{14}{5}, -1) \)
3. \( (-1, \infty) \)
**Testing the intervals:**
1. **Interval \( (-\infty, -\frac{14}{5}) \)**: Choose \( x = -3 \):
\[
\frac{5(-3) + 14}{-3 + 1} = \frac{-15 + 14}{-2} = \frac{-1}{-2} = \frac{1}{2} > 0
\]
This interval satisfies the inequality.
2. **Interval \( (-\frac{14}{5}, -1) \)**: Choose \( x = -2 \):
\[
\frac{5(-2) + 14}{-2 + 1} = \frac{-10 + 14}{-1} = \frac{4}{-1} = -4 < 0
\]
This interval does not satisfy the inequality.
3. **Interval \( (-1, \infty) \)**: Choose \( x = 0 \):
\[
\frac{5(0) + 14}{0 + 1} = \frac{14}{1} = 14 > 0
\]
This interval satisfies the inequality.
**Including the critical points:**
- At \( x = -\frac{14}{5} \):
\[
\frac{5(-\frac{14}{5}) + 14}{-\frac{14}{5} + 1} = \frac{-14 + 14}{-\frac{14}{5} + 1} = \frac{0}{-\frac{9}{5}} = 0
\]
This point is included since the inequality is non-strict (≥).
- At \( x = -1 \), the expression is undefined, so this point is not included.
**Final solution:**
The solution to the inequality is:
\[
(-\infty, -1) \cup \left[-\frac{14}{5}, \infty\right)
\]
Thus, the final answer is:
\[
\boxed{(-\infty, -1) \cup \left[-\frac{14}{5}, \infty\right)}
\]
Quick Answer
\[
(-\infty, -1) \cup \left[-\frac{14}{5}, \infty\right)
\]
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