Solve Absolute Value Inequality: |3x - 1| < 5x Analysis

Absolute Value Inequalities with Case Analysis

Given:

3x1<5x \left|3x - 1\right| < 5x

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:

3x1<5x \left|3x - 1\right| < 5x

Which of the following statements is necessarily true?

2

Step-by-step solution

Let's solve the inequality 3x1<5x \left|3x - 1\right| < 5x :

  1. Remove the absolute value by considering two cases:

    1. 3x1<5x 3x - 1 < 5x
      Solve for x x :

    2. 3x1<5x 3x - 1 < 5x

      Subtract 3x 3x from both sides:
      1<2x -1 < 2x

      Divide both sides by 2 2 :
      12<x -\frac{1}{2} < x

      Rewriting this inequality yields: x>12 x > -\frac{1}{2}

    3. (3x1)<5x -(3x - 1) < 5x
      Simplifying yields:

    4. 3x+1<5x -3x + 1 < 5x

      Add 3x 3x to both sides:
      1<8x 1 < 8x

      Divide both sides by 8 8 :
      18<x \frac{1}{8} < x

      This implies x>18 x > \frac{1}{8}

  2. Combine results:

  3. Both conditions imply x>18 x > \frac{1}{8} . Thus, the solution is x>18 x > \frac{1}{8} .

3

Final Answer

x>18 x > \frac{1}{8}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Consider both positive and negative cases when solving absolute value inequalities
  • Technique: For |3x - 1| < 5x, solve 3x - 1 < 5x and -(3x - 1) < 5x separately
  • Check: Test x = 1/4: |3(1/4) - 1| = 1/4 < 5(1/4) = 5/4 ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to consider the negative case
    Don't solve only 3x - 1 < 5x = wrong solution x > -1/2! This ignores when the expression inside is negative. Always solve both cases: the positive case AND the negative case -(3x - 1) < 5x.

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 solve two cases for absolute value inequalities?

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The absolute value |3x - 1| means the distance from zero. This expression could be positive OR negative, so we must consider both possibilities to find all solutions.

How do I know which case applies to my solution?

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You don't choose one case! You solve both cases and then find where they overlap. The final answer is where both conditions are satisfied.

What if I get different answers from the two cases?

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That's normal! Case 1 gave us x>12 x > -\frac{1}{2} and Case 2 gave us x>18 x > \frac{1}{8} . The solution is the more restrictive condition: x>18 x > \frac{1}{8} .

Can the right side of the inequality be negative?

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Great question! Since absolute values are always non-negative, if 5x < 0 (when x < 0), then there's no solution because we can't have |something| < negative number.

How do I verify my final answer?

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Pick a test value like x=14 x = \frac{1}{4} : 3(14)1=14=14 |3(\frac{1}{4}) - 1| = |\frac{1}{4}| = \frac{1}{4} and 5(14)=54 5(\frac{1}{4}) = \frac{5}{4} . Since 14<54 \frac{1}{4} < \frac{5}{4} , it works!

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