Mathematics 9709 · AS & A Level · Complex numbers

Complex numbers — practice question

(a(i))[2]

The complex number $u$ is given by $u = \frac{5}{a + 2i}$, where $a$ is a real constant. Write $u$ in the form $x + iy$, with $x$ and $y$ both real.

(a(ii))[3]

Determine the value of $a$ such that $\arg(u^*) = \frac{3}{4}\pi$, where $u^*$ is the complex conjugate of $u$.

(b)[4]

On a sketch of an Argand diagram, shade the area containing the complex numbers $z$ that satisfy both $|z| < 2$ and $|z| < |z - 2 - 2i|$.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Multiply the numerator and denominator by $a-2i$, or an equivalent expression

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