Complex Modulus of Product of Complex Numbers

Theorem
Let $z_1, z_2 \in \C$ be complex numbers.

Let $\cmod z$ be the modulus of $z$.

Then:
 * $\cmod {z_1 z_2} = \cmod {z_1} \cdot \cmod {z_2}$

Also see

 * Absolute Value Function is Completely Multiplicative