If z = x + i y, then the area of the triangle whose vertices are points z, iz and z + iz is
BC = AD = |z|
CD = AB = |z|
We want to find the area of the triangle ABD. It is a right-angled triangle wid A = 90∘
⇒ Area = 12 × AB × AD
= 12 |z| × |z|
= 12 |z|2