Question
Answer Key
Worked Solution
9758/2022/P1/Q01
Do not use a calculator in answering this question.
The complex numbers (z) and (w) satisfy the following equations.
$$\mathrm{i} z+2 w=-1$$
$$(2-\mathrm{i}) z+\mathrm{i} w=6$$
Find (z) and (w), giving your answers in the form $(a+\mathrm{i} b)$ where $a$ and $b$ are real numbers.
[4]
$z=2+i, w=-i$
$\begin{aligned}
-z + 2 i w &=-i \\2 i w &=z-i
\\ i w &=\frac{1}{2}(z-i) — (1)
\\ \text { sub (1) in the second given equation }
\\(2-i) z+\frac{1}{2}(z-i) &=6 \\\left(2-i+\frac{1}{2}\right) z &=6+\frac{1}{2} i \\\left(\frac{5}{2}-i\right) z &=6+\frac{1}{2} i \\(5-2 i) z &=12+i
\end{aligned}$
$$\\ z =\frac{12+i}{5-2 i} \times \frac{5+2 i}{5+2 i}=2+i$$
$\begin{aligned}
\\ \Rightarrow 2 i-1 &+2 w=-1
\\ w &=-i
\end{aligned}$