# Math Help - covariance inequality

1. ## covariance inequality

Show that $Cov(X,Y)^{2} \le Var(X)Var(Y)$

It seems like it should be simple enough but I can't seem to get anywhere. I've expanded it all in terms of expected values but it doesn't seem immediately obvious how to prove the inequality.

2. Cauchy-Schwartz Inequality

3. Ah, I had no idea it applied to expectation. Thanks.