Solve |5x - 2| ≤ 3x + 4: Absolute Value Inequality Challenge

Absolute Value Inequalities with Linear Bounds

Given:

5x23x+4 \left|5x - 2\right| \leq 3x + 4

Which of the following statements is necessarily true?

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Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given:

5x23x+4 \left|5x - 2\right| \leq 3x + 4

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve the problem, we'll follow these steps:

  • Step 1: Solve the inequality 5x23x+4 \left|5x - 2\right| \leq 3x + 4 by considering two cases.
  • Step 2: Combine the solutions of both cases to find the intersection of permissible values for x x .

Step 1: Consider the inequality (3x+4)5x23x+4 - (3x + 4) \leq 5x - 2 \leq 3x + 4 .
Case 1: Solve 5x2(3x+4) 5x - 2 \geq -(3x + 4) , which simplifies to:
5x23x4 5x - 2 \geq -3x - 4
Add 3x 3x to both sides:
8x24 8x - 2 \geq -4
Add 2 to both sides:
8x2 8x \geq -2
Divide by 8:
x14 x \geq -\frac{1}{4}

Step 2: Now solve 5x23x+4 5x - 2 \leq 3x + 4 to get:
Subtract 3x 3x from both sides:
2x24 2x - 2 \leq 4
Add 2 to both sides:
2x6 2x \leq 6
Divide by 2:
x3 x \leq 3

Step 3: Combine solutions from Case 1 and Case 2.
14x3 -\frac{1}{4} \leq x \leq 3

Therefore, the solution to the problem is: 14x3-\frac{1}{4} \le x \le 3.

3

Final Answer

14x3 -\frac{1}{4} \le x \le 3

Key Points to Remember

Essential concepts to master this topic
  • Rule: For |A| ≤ B, solve -B ≤ A ≤ B as compound inequality
  • Technique: Split into two inequalities: 5x - 2 ≥ -(3x + 4) and 5x - 2 ≤ 3x + 4
  • Check: Test boundary values x = -1/4 and x = 3 in original inequality ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting the negative bound constraint
    Don't solve only |5x - 2| ≤ 3x + 4 as 5x - 2 ≤ 3x + 4 = incomplete solution! This ignores the negative case and misses half the inequality. Always remember |A| ≤ B means -B ≤ A ≤ B, requiring both bounds.

Practice Quiz

Test your knowledge with interactive questions

Given:

\( \left|2x-1\right|>-10 \)

Which of the following statements is necessarily true?

FAQ

Everything you need to know about this question

Why do I need to solve two separate inequalities?

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The absolute value 5x2 |5x - 2| can equal either 5x - 2 or -(5x - 2) depending on whether the expression inside is positive or negative. You need both cases to find the complete solution!

How do I know which values to test in my final answer?

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Always test the boundary values from your solution interval. For 14x3 -\frac{1}{4} \leq x \leq 3 , test x = -1/4, x = 3, and one value in between like x = 1.

What if 3x + 4 becomes negative?

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Great question! If 3x+4<0 3x + 4 < 0 (when x < -4/3), then the inequality 5x23x+4 |5x - 2| \leq 3x + 4 has no solution because absolute values are always non-negative.

Can I solve this by graphing instead?

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Yes! Graph y=5x2 y = |5x - 2| and y=3x+4 y = 3x + 4 , then find where the absolute value function is below or equal to the linear function.

Why is my answer an interval instead of a single number?

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Unlike equations which typically have specific solutions, inequalities usually have ranges of values that work. The solution 14x3 -\frac{1}{4} \leq x \leq 3 means all numbers between -1/4 and 3 satisfy the inequality!

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