Solve |2x + 1| > 3: Absolute Value Inequality Step-by-Step

Absolute Value Inequalities with Case Analysis

Given:

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

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

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve 2x+1>3 \left| 2x + 1 \right| > 3 , consider the two cases for the absolute value: 2x+1>3 2x + 1 > 3 and 2x+1<3 2x + 1 < -3 .

1. Solving 2x+1>3 2x + 1 > 3 :

2x+1>3 2x + 1 > 3

Subtract 1 from both sides:

2x>2 2x > 2

Divide both sides by 2:

x>1 x > 1

2. Solving 2x+1<3 2x + 1 < -3 :

2x+1<3 2x + 1 < -3

Subtract 1 from both sides:

2x<4 2x < -4

Divide both sides by 2:

x<2 x < -2

Thus, the solution isx<2 or x>1 x < -2 \text{ or } x > 1 .

3

Final Answer

x<2 or x>1 x < -2 \text{ or } x > 1

Key Points to Remember

Essential concepts to master this topic
  • Rule: Split absolute value inequality into two separate cases
  • Technique: For |expression| > 3, solve expression > 3 AND expression < -3
  • Check: Test boundary values: x = -2 gives |2(-2)+1| = 3, not > 3 ✓

Common Mistakes

Avoid these frequent errors
  • Writing the solution as an intersection instead of union
    Don't write x < -2 AND x > 1 = impossible solution! This creates a contradiction since no number can be both less than -2 and greater than 1 simultaneously. Always use OR (union) to combine the two cases for 'greater than' absolute value inequalities.

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 we get two separate cases for absolute value inequalities?

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The absolute value 2x+1|2x + 1| measures distance from zero. When this distance is greater than 3, the expression inside could be either greater than 3 or less than -3.

How do I know when to use AND versus OR?

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For 'greater than' inequalities like expression>3|expression| > 3, use OR because you want values that satisfy either case. For 'less than' inequalities, use AND.

What's the difference between > and ≥ in the final answer?

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Since our original inequality uses >> (not ≥), the boundary points where 2x+1=3|2x + 1| = 3 are not included. That's why we use x<2x < -2 and x>1x > 1, not ≤ or ≥.

How can I visualize this solution?

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Draw a number line! Mark points at x = -2 and x = 1 with open circles (not included). Shade everything to the left of -2 and everything to the right of 1.

Can I check my answer by plugging in test values?

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Absolutely! Try x=3x = -3: 2(3)+1=5=5>3|2(-3) + 1| = |-5| = 5 > 3 ✓. Try x=2x = 2: 2(2)+1=5=5>3|2(2) + 1| = |5| = 5 > 3 ✓. Try x=0x = 0: 2(0)+1=1=1<3|2(0) + 1| = |1| = 1 < 3

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