Solve |5x - 7| > 2x + 1: Absolute Value Inequality Challenge

Absolute Value Inequalities with Two-Case Analysis

Given:

5x7>2x+1 \left|5x - 7\right| > 2x + 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:

5x7>2x+1 \left|5x - 7\right| > 2x + 1

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve the inequality 5x7>2x+1 \left|5x - 7\right| > 2x + 1 , we consider two scenarios for the absolute value expression.

Case 1: 5x7>2x+1 5x - 7 > 2x + 1

Rearrange terms:

5x2x>1+7 5x - 2x > 1 + 7

3x>8 3x > 8

x>83 x > \frac{8}{3}

Case 2: (5x7)>2x+1 -(5x - 7) > 2x + 1

This simplifies to:

5x+7>2x+1 -5x + 7 > 2x + 1

Rearrange terms:

71>2x+5x 7 - 1 > 2x + 5x

6>7x 6 > 7x

x<67 x < \frac{6}{7}

Hence, the solution combines both cases as:

x<67 or x>83 x < \frac{6}{7} \text{ or } x > \frac{8}{3}

3

Final Answer

x<67 or x>83 x < \frac{6}{7} \text{ or } x > \frac{8}{3}

Key Points to Remember

Essential concepts to master this topic
  • Definition: |expression| > value means two separate cases to solve
  • Technique: Case 1: 5x - 7 > 2x + 1, Case 2: -(5x - 7) > 2x + 1
  • Check: Test x = 0: |5(0) - 7| = 7 > 2(0) + 1 = 1 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting the negative case when opening absolute value
    Don't just solve 5x - 7 > 2x + 1 and stop = missing half the solution! The absolute value creates two scenarios: positive and negative expressions. Always solve both cases: when the inside is positive AND when it's negative.

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 two cases for absolute value inequalities?

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Because absolute value measures distance from zero! When 5x7>2x+1 |5x - 7| > 2x + 1 , either 5x - 7 is positive and greater than 2x + 1, OR 5x - 7 is negative and its opposite is greater than 2x + 1.

How do I know when to use 'or' versus 'and' in my final answer?

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For absolute value inequalities with 'greater than' (>), use 'or' because values can satisfy either case. For 'less than' (<), you typically use 'and' because values must be between the boundaries.

What if one of my cases gives an impossible result?

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That's normal! Sometimes one case yields no solution or contradicts the other. Simply ignore the impossible case and use only the valid solutions in your final answer.

How can I check if my solution intervals are correct?

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Pick a test value from each interval and substitute into the original inequality. For example, try x = 0 (from x<67 x < \frac{6}{7} ) and x = 3 (from x>83 x > \frac{8}{3} ) to verify they work!

Why is the solution written as two separate intervals?

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Because the values that make the inequality true are not continuous! There's a gap between 67 \frac{6}{7} and 83 \frac{8}{3} where the inequality is false, so we write the solution as two separate regions.

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