The complex number $u = \dfrac{1}{-2+i}$ . Find $|u|$ .

\dfrac{1}{5}

\dfrac{2}{5}

\sqrt{5}

\dfrac{\sqrt{5}}{5}

Explanation

|u|=\tfrac{1}{|-2+i|}=\tfrac{1}{\sqrt5}=\tfrac{\sqrt5}{5}

Derived from ZIMSEC Mathematics Paper 1, November 2016, Q1

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