Math Problem Statement

Solve the polynomial inequality: -4(x + 8)(x + 7)(x + 3) < 0.

Solution

Let's solve the inequality 4(x+8)(x+7)(x+3)<0-4(x + 8)(x + 7)(x + 3) < 0.

Step 1: Simplify the inequality

Since 4-4 is a constant negative number, we can divide both sides of the inequality by 4-4, but remember that dividing by a negative number reverses the inequality sign.

(x+8)(x+7)(x+3)>0(x + 8)(x + 7)(x + 3) > 0

Now we need to solve (x+8)(x+7)(x+3)>0(x + 8)(x + 7)(x + 3) > 0.

Step 2: Find the roots of the polynomial

The expression is already factored, and the roots (values of xx where the product equals 0) are:

  • x=8x = -8
  • x=7x = -7
  • x=3x = -3

These roots divide the number line into four intervals:

  • (,8)(-\infty, -8)
  • (8,7)(-8, -7)
  • (7,3)(-7, -3)
  • (3,)(-3, \infty)

Step 3: Test the sign of the expression in each interval

We will test the sign of (x+8)(x+7)(x+3)(x + 8)(x + 7)(x + 3) in each interval by picking test points within these intervals.

  1. For x<8x < -8 (choose x=9x = -9): (x+8)(x+7)(x+3)=(9+8)(9+7)(9+3)=(1)(2)(6)=12(negative)(x + 8)(x + 7)(x + 3) = (-9 + 8)(-9 + 7)(-9 + 3) = (-1)(-2)(-6) = -12 \quad (\text{negative})

  2. For 8<x<7-8 < x < -7 (choose x=7.5x = -7.5): (7.5+8)(7.5+7)(7.5+3)=(0.5)(0.5)(4.5)=1.125(positive)(-7.5 + 8)(-7.5 + 7)(-7.5 + 3) = (0.5)(-0.5)(-4.5) = 1.125 \quad (\text{positive})

  3. For 7<x<3-7 < x < -3 (choose x=5x = -5): (5+8)(5+7)(5+3)=(3)(2)(2)=12(negative)(-5 + 8)(-5 + 7)(-5 + 3) = (3)(2)(-2) = -12 \quad (\text{negative})

  4. For x>3x > -3 (choose x=0x = 0): (0+8)(0+7)(0+3)=(8)(7)(3)=168(positive)(0 + 8)(0 + 7)(0 + 3) = (8)(7)(3) = 168 \quad (\text{positive})

Step 4: Determine the solution

We want the expression to be positive, so we select the intervals where the sign is positive.

The solution is: (8,7)(3,)(-8, -7) \cup (-3, \infty)

Final Answer:

x(8,7)(3,)x \in (-8, -7) \cup (-3, \infty)

Would you like more details on any part of the solution, or do you have any questions?

Here are five questions that can expand on this:

  1. How does the constant factor 4-4 influence the inequality?
  2. What happens if the inequality sign is changed to \leq instead of <<?
  3. Can this solution be visualized graphically?
  4. How would you handle this inequality if the polynomial were not factored?
  5. What are other methods to solve polynomial inequalities?

Tip: Always remember to reverse the inequality sign when dividing or multiplying by a negative number.

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Math Problem Analysis

Mathematical Concepts

Algebra
Polynomial Inequalities

Formulas

Sign analysis of polynomial products

Theorems

Sign analysis for intervals of polynomial roots

Suitable Grade Level

Grades 10-12