2) Solve each inequality algebraically. d. x3 – x > 0

Algebra: Structure And Method, Book 1
(REV)00th Edition
ISBN:9780395977224
Author:Richard G. Brown, Mary P. Dolciani, Robert H. Sorgenfrey, William L. Cole
Publisher:Richard G. Brown, Mary P. Dolciani, Robert H. Sorgenfrey, William L. Cole
Chapter2: Working With Real Numbers
Section2.9: Dividing Real Numbers
Problem 10MRE
Question
**Problem:** Solve each inequality algebraically.

**Inequality:** \( x^3 - x \geq 0 \)

**Solution:** This inequality can be factored and solved using the following steps:

1. **Factor the Expression:**

   Factor \( x^3 - x \) by taking out the common factor \( x \):

   \[
   x^3 - x = x(x^2 - 1)
   \]

   Recognize that \( x^2 - 1 \) can be further factored as a difference of squares:

   \[
   x(x^2 - 1) = x(x - 1)(x + 1)
   \]

2. **Determine Critical Points:**

   Set each factor equal to zero to find critical points:

   \[
   x = 0, \quad x - 1 = 0 \quad \Rightarrow \quad x = 1, \quad x + 1 = 0 \quad \Rightarrow \quad x = -1
   \]

   The critical points are \( x = -1, 0, 1 \).

3. **Test Intervals:**

   Test intervals determined by critical points in the inequality \( x(x - 1)(x + 1) \geq 0 \):

   - Interval \( (-\infty, -1) \)
   - Interval \( (-1, 0) \)
   - Interval \( (0, 1) \)
   - Interval \( (1, \infty) \)

4. **Analyze Signs in Each Interval:**

   - \( x \in (-\infty, -1) \): Choose \( x = -2 \), then \((-2)(-3)(-1) < 0\)
   - \( x \in (-1, 0) \): Choose \( x = -0.5 \), then \((-0.5)(-1.5)(0.5) > 0\)
   - \( x \in (0, 1) \): Choose \( x = 0.5 \), then \((0.5)(-0.5)(1.5) < 0\)
   - \( x \in (1, \infty) \): Choose \( x = 2 \), then \((2)(1)(3) > 0\)
Transcribed Image Text:**Problem:** Solve each inequality algebraically. **Inequality:** \( x^3 - x \geq 0 \) **Solution:** This inequality can be factored and solved using the following steps: 1. **Factor the Expression:** Factor \( x^3 - x \) by taking out the common factor \( x \): \[ x^3 - x = x(x^2 - 1) \] Recognize that \( x^2 - 1 \) can be further factored as a difference of squares: \[ x(x^2 - 1) = x(x - 1)(x + 1) \] 2. **Determine Critical Points:** Set each factor equal to zero to find critical points: \[ x = 0, \quad x - 1 = 0 \quad \Rightarrow \quad x = 1, \quad x + 1 = 0 \quad \Rightarrow \quad x = -1 \] The critical points are \( x = -1, 0, 1 \). 3. **Test Intervals:** Test intervals determined by critical points in the inequality \( x(x - 1)(x + 1) \geq 0 \): - Interval \( (-\infty, -1) \) - Interval \( (-1, 0) \) - Interval \( (0, 1) \) - Interval \( (1, \infty) \) 4. **Analyze Signs in Each Interval:** - \( x \in (-\infty, -1) \): Choose \( x = -2 \), then \((-2)(-3)(-1) < 0\) - \( x \in (-1, 0) \): Choose \( x = -0.5 \), then \((-0.5)(-1.5)(0.5) > 0\) - \( x \in (0, 1) \): Choose \( x = 0.5 \), then \((0.5)(-0.5)(1.5) < 0\) - \( x \in (1, \infty) \): Choose \( x = 2 \), then \((2)(1)(3) > 0\)
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