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

Absolute Value Inequalities with Case Analysis

Given:

2x+34x2 \left|2x + 3\right| \leq 4x - 2

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:

2x+34x2 \left|2x + 3\right| \leq 4x - 2

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve the inequality 2x+34x2 \left|2x + 3\right| \leq 4x - 2 , we can consider two cases for the absolute value expression.

Case 1: 2x+34x2 2x + 3 \leq 4x - 2

Rearrange terms:

3+24x2x 3 + 2 \leq 4x - 2x

52x 5 \leq 2x

x52 x \geq \frac{5}{2}

Case 2: (2x+3)4x2 -(2x + 3) \leq 4x - 2

This simplifies to:

2x34x2 -2x - 3 \leq 4x - 2

Rearrange terms:

3+24x+2x -3 + 2 \leq 4x + 2x

16x -1 \leq 6x

x16 x \geq \frac{-1}{6}

Combining both conditions, the necessary true statement is:

x52 x \geq \frac{5}{2}

3

Final Answer

x52 x \geq \frac{5}{2}

Key Points to Remember

Essential concepts to master this topic
  • Critical Requirement: Right side must be non-negative for any solution
  • Case Method: Consider both |u| = u when u ≥ 0 and |u| = -u when u < 0
  • Verification: Check x ≥ 5/2 satisfies both 4x - 2 ≥ 0 and original inequality ✓

Common Mistakes

Avoid these frequent errors
  • Solving cases without checking domain restrictions
    Don't just solve 2x + 3 ≤ 4x - 2 and -(2x + 3) ≤ 4x - 2 separately = invalid solutions! The absolute value inequality requires 4x - 2 ≥ 0 for any solution to exist. Always verify the right side is non-negative first.

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 check if 4x - 2 ≥ 0?

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Because absolute values are always non-negative! If |2x + 3| ≤ 4x - 2, then 4x - 2 must be ≥ 0. Otherwise, you'd have something ≥ 0 being less than or equal to something < 0, which is impossible.

What's the difference between the two cases?

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Case 1: When 2x + 3 ≥ 0, so |2x + 3| = 2x + 3
Case 2: When 2x + 3 < 0, so |2x + 3| = -(2x + 3). You need both cases to cover all possible values of x.

Why is the final answer x ≥ 5/2 and not x ≥ -1/6?

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You must satisfy all conditions simultaneously! From Case 1: x ≥ 5/2, from Case 2: x ≥ -1/6, and from the domain: x ≥ 1/2. The intersection of all these is x ≥ 5/2.

How do I know which case applies to my answer?

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After finding the solution, substitute back to check! For x ≥ 5/2, we have 2x + 3 ≥ 8, so 2x + 3 > 0, confirming Case 1 applies to our final answer.

What if I get no solution?

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That's possible! If the domain restriction 4x20 4x - 2 \geq 0 doesn't overlap with either case solution, then the inequality has no solution. Always check this carefully.

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