Solve |2x + 3| > 4x + 1: Absolute Value Inequality Challenge

Absolute Value Inequalities with Two-Case Analysis

Given:

2x+3>4x+1 \left|2x + 3\right| > 4x + 1

Which of the following statements is necessarily true?

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Step-by-step written solution

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1

Understand the problem

Given:

2x+3>4x+1 \left|2x + 3\right| > 4x + 1

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve 2x+3>4x+1 \left|2x + 3\right| > 4x + 1 , we need to consider two cases based on the definition of absolute value:

1. 2x+3>4x+1 2x + 3 > 4x + 1

2. 2x+3<(4x+1) 2x + 3 < -(4x + 1)

Solving the first inequality:

2x+3>4x+13>4x2x+13>2x+12>2xx<1 2x + 3 > 4x + 1 \Rightarrow 3 > 4x - 2x + 1 \Rightarrow 3 > 2x + 1 \Rightarrow 2 > 2x \Rightarrow x < 1

Solving the second inequality:

2x+3<4x16x<4x<23 2x + 3 < -4x - 1 \Rightarrow 6x < -4 \Rightarrow x < -\frac{2}{3}

These inequalities indicate that x<1 x < 1 is the range that satisfies the original inequality.

3

Final Answer

x<1 x < 1

Key Points to Remember

Essential concepts to master this topic
  • Definition: Split |expression| > value into two separate inequality cases
  • Technique: Case 1: 2x + 3 > 4x + 1, Case 2: 2x + 3 < -(4x + 1)
  • Check: Test x = 0: |3| > 1 is true, confirming x < 1 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to consider both positive and negative cases
    Don't solve |2x + 3| > 4x + 1 as just 2x + 3 > 4x + 1 = incomplete solution! The absolute value creates two scenarios that must both be checked. Always split into both 2x + 3 > 4x + 1 AND 2x + 3 < -(4x + 1) cases.

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 consider two cases for absolute value inequalities?

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The absolute value |expression| means the distance from zero, which is always positive. So |2x + 3| could equal either (2x + 3) when it's positive, or -(2x + 3) when it's negative!

How do I know which case applies to my answer?

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You don't choose! You solve both cases and then combine the results. The final answer includes all x-values that satisfy either case.

What does the negative case 2x + 3 < -(4x + 1) really mean?

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This case handles when the expression inside the absolute value bars (2x + 3) is negative. We flip it to positive by multiplying by -1, so |2x + 3| becomes -(2x + 3).

Why is x < 1 the final answer instead of combining both results?

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Great question! When we solve case 1, we get x < 1. Case 2 gives x < -2/3. Since every number less than -2/3 is also less than 1, the broader condition x < 1 includes both cases.

How can I verify my answer is correct?

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Pick a test value! Try x = 0: 2(0)+3=3 |2(0) + 3| = 3 and 4(0)+1=1 4(0) + 1 = 1 . Since 3 > 1, our solution x < 1 works! ✓

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