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The set of all x satisfying the inequality \(|3 - 4x| \le 11\) is

  • A.\([-2, 7]\)
  • B.\(\left[-2, \frac{7}{2}\right]\)
  • C.\([-7, 2]\)
  • D.\(\left[\frac{-7}{2}, 2\right]\)
  • E.\([-2, -2]\)

Answer: B

The solution set is \(\left[-2, \frac{7}{2}\right]\).

\(|u| \le 11\) means \(-11 \le u \le 11\):

\[ \begin{aligned} -11 \le 3 - 4x &\le 11 \\ -14 \le -4x &\le 8 \\ -2 \le x &\le \tfrac{7}{2} \end{aligned} \]

Dividing by \(-4\) reverses both inequalities. Check: \(x = -2\) gives \(|11| = 11\) and \(x = 3.5\) gives \(|-11| = 11\). \([-2, 7]\) forgets to divide 14 by 4, and the other intervals have the signs reversed.

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