Math Help - complex numbers problem

1. complex numbers problem

How would you go about showing this?

2. Just multiply and collect terms: $\left[ {\left( {a + bi} \right)+\left( {c + di} \right)} \right]\left[ {\left( {a - bi} \right)+\left( {c - di} \right)} \right]$

3. Hello,
Originally Posted by Haris

How would you go about showing this?
You can do it in two ways.

1st :
Write z and w with their real and imaginary parts and expand the LHS

2nd :
Use these rules :
$z\bar z=|z|^2$ for any complex number
$z+\bar z=2 \ \Re(z)$
$\bar z+\bar w=\overline{z+w}$
and then expand the LHS

There is another rule, but you don't need it here :
$z-\bar z=2 \ \Im(z)$