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If \(x \ne 11\) satisfies the inequality \(\frac{2x - 21}{x - 11} \ge 3\),then x lies in the interval

  • A.\((-\infty, 11)\)
  • B.\((11, 12]\)
  • C.\((11, 12)\)
  • D.\((11, \infty)\)
  • E.\([12, \infty)\)

Answer: B

\(x\) lies in \((11, 12]\).

Move everything to one side over the common denominator:

\[ \frac{2x - 21}{x - 11} - 3 = \frac{12 - x}{x - 11} \ge 0 \]

The fraction is non-negative when numerator and denominator have the same sign (or the numerator is 0): \(12 - x \ge 0\) with \(x - 11 \gt 0\) gives \(11 \lt x \le 12\); the other case is impossible. 12 itself is included (the fraction equals 0); 11 is not. Multiplying through by \(x - 11\) without checking its sign leads to the wrong intervals.

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