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

Absolute Value Inequalities with Split Cases

Given:

2x+1>7 |2x + 1| > 7

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>7 |2x + 1| > 7

Which of the following statements is necessarily true?

2

Step-by-step solution

To solve the inequality 2x+1>7 |2x + 1| > 7 , we split it into two separate inequalities:

2x+1>7 2x + 1 > 7 or 2x+1<7 2x + 1 < -7 .

For the first inequality 2x+1>7 2x + 1 > 7 , subtract 1 from both sides:

2x>6 2x > 6

Divide by 2:

x>3 x > 3

For the second inequality 2x+1<7 2x + 1 < -7 , subtract 1 from both sides:

2x<8 2x < -8

Divide by 2:

x<4 x < -4

Therefore, the solution is x>3 x > 3 or x<4 x < -4 .

3

Final Answer

x>3 x > 3 or x<4 x < -4

Key Points to Remember

Essential concepts to master this topic
  • Rule: Split absolute value inequalities into two separate cases
  • Technique: For |expression| > number, solve expression > number OR expression < -number
  • Check: Test values: x = 4 gives |9| = 9 > 7 ✓, x = 0 gives |1| = 1 < 7 ✗

Common Mistakes

Avoid these frequent errors
  • Using AND instead of OR to connect solutions
    Don't write x > 3 AND x < -4 = impossible condition! No number can be both greater than 3 and less than -4 simultaneously. Always use OR to connect the two solution intervals for 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 split the absolute value into two cases?

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The absolute value measures distance from zero, so 2x+1>7 |2x + 1| > 7 means the expression inside is either more than 7 units positive OR more than 7 units negative from zero.

How do I know when to use OR versus AND?

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For absolute value inequalities with greater than (>), always use OR. The solution is two separate regions on the number line. For less than (<), you'd use AND because the solution would be between two values.

Why is the answer not between -4 and 3?

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That would be the solution to 2x+1<7 |2x + 1| < 7 ! Since we have greater than 7, we want values that make the absolute value large, which happens at the extremes of the number line.

How can I check if x = 4 works?

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Substitute: 2(4)+1=9=9 |2(4) + 1| = |9| = 9 . Since 9 > 7, x = 4 is in our solution set! Try x = 0: 1=1<7 |1| = 1 < 7 , so it's not a solution.

What does the solution look like on a number line?

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Draw two arrows: one pointing left from -4 (not including -4) and one pointing right from 3 (not including 3). The solution includes all numbers in these two regions.

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