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June 2017 p33 q11
1967
(a) The complex numbers z and w satisfy the equations
\(z + (1+i)w = i\)
and
\((1-i)z + iw = 1\).
Solve the equations for z and w, giving your answers in the form x + iy, where x and y are real.
(b) The complex numbers u and v are given by \(u = 1 + (2\sqrt{3})i\) and \(v = 3 + 2i\). In an Argand diagram, u and v are represented by the points A and B. A third point C lies in the first quadrant and is such that \(BC = 2AB\) and angle \(\angle ABC = 90^\circ\). Find the complex number z represented by C, giving your answer in the form x + iy, where x and y are real and exact.
Solution
(a) Solve for \(z\) or \(w\):
Use \(i^2 = -1\).
Obtain \(w = \frac{i}{2-i}\) or \(= \frac{2+i}{2-i}\).
Multiply numerator and denominator by the conjugate of the denominator.
Obtain \(w = -\frac{1}{5} + \frac{4}{5}i\).
Obtain \(z = \frac{3}{5} + \frac{4}{5}i\).
(b) EITHER:
Find \(\pm \left[ 2 + (2 - 2\sqrt{3})i \right]\).
Multiply by \(2i\) (or \(-2i\)).
Add result to \(v\).
Obtain answer \(4\sqrt{3} - 1 + 6i\).
OR:
State \(\frac{z-v}{v-u} = ki\), or equivalent.
State \(k = 2\).
Substitute and solve for \(z\) even if \(i\) omitted.