If z1 and z2 are two complex number and a,b are two real numbers, then
|az1−bz2|2+|bz1+az2|2 equals
2ab
|az1−bz2|2+|bz1+az2|2
= a2|z1|2+b2|z2|2−abz1¯¯¯¯¯z2−ab¯¯¯¯¯z1z2+b2|z1|2+a2|z2|2+baz1¯¯¯¯¯z2+ba¯¯¯¯¯z1z2
= (a2+b2)(|z1|2+|z2|2)
we have
For any two complex numbers z1z2 and any two real numbers a and b |az1−bz2|2+|bz1+az2|2 =