The complex number z is defined by z = a + ib, where a and b are real. The complex conjugate of z is denoted by z*.
- Show that |z|2 = zz* and that (z - ki)* = z* + ki, where k is real.
\(In an Argand diagram a set of points representing complex numbers z is defined by the equation |z - 10i| = 2|z - 4i|.\)
- Show, by squaring both sides, that zz* - 2iz* + 2iz - 12 = 0. Hence show that |z - 2i| = 4.
- Describe the set of points geometrically.
Solution
(i) For \(|z|^2 = zz*\), we have \(z = a + ib\) and \(z* = a - ib\). Thus, \(|z|^2 = (a + ib)(a - ib) = a^2 + b^2\).
For \((z - ki)* = z* + ki\), we have \(z - ki = a + ib - ki\). The conjugate is \((a + ib - ki)^* = a - ib + ki\).
(ii) Start with \(|z - 10i| = 2|z - 4i|\). Square both sides: \((z - 10i)(z^* + 10i) = 4(z - 4i)(z^* + 4i)\).
Expand and simplify to get \(zz* - 2iz* + 2iz - 12 = 0\).
Rearrange to find \(|z - 2i| = 4\).
(iii) The equation \(|z - 2i| = 4\) represents a circle in the Argand diagram with center at \(2i\) and radius 4.
Log in to record attempts.