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The domain of the function \(f(x) = \sqrt{7 - 11x}\) is

  • A.\((-\infty, -1]\)
  • B.\(\left[\frac{7}{11}, \infty\right)\)
  • C.\(\left(-\infty, \frac{7}{11}\right]\)
  • D.\(\left[\frac{7}{11}, 1\right]\)
  • E.\([-1, 1]\)

Answer: C

The domain is \(\left(-\infty, \frac{7}{11}\right]\).

A square root is real only when its argument is non-negative:

\[ 7 - 11x \ge 0 \;\Rightarrow\; x \le \frac{7}{11} \]

So every \(x\) up to and including \(7/11\) is allowed. \(\left[\frac{7}{11}, \infty\right)\) reverses the inequality (the sign flips only when dividing by a negative number, which is not done here), and \((-\infty, -1]\), \(\left[\frac{7}{11}, 1\right]\) and \([-1, 1]\) are only parts of the domain or lie outside it.

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