Multiplication Property of Characteristic Functions

Theorem
Let $X$ and $Y$ be independent random variables on a probability space $\left({\Omega, \Sigma, \Pr}\right)$.

Let $\phi_X$ and $\phi_Y$ denote the characteristic functions of $X$ and $Y$ respectively.

Then:
 * $\displaystyle \phi_{X+Y} = \phi_X\phi_Y$

Proof
Let $i = \sqrt{-1}$.

Let $E$ be the expectation operator.

Hence:
 * $\displaystyle \phi_{X+Y} = \phi_X\phi_Y$