# Thread: Covariance

1. ## Covariance

Let
X be a random variable taking the values ±1 and ±2 with equal probability. Let Y = X^2.

How do i calculate the Cov(X,Y)?
i'm not sure which formula to use because ive tried Cov(X,Y) = E(XY)-(E(X)E(Y))
but that equals 0

2. i think i might of figured this one out the covariance is 0 because the random variables are independent?

3. Originally Posted by dexza666
i think i might of figured this one out the covariance is 0 because the random variables are independent?
Yes !

$\text{X and Y are independent } \Longleftrightarrow \text{ cov}(X,Y)=0$

But here, I'm not sure they're independent... you gotta prove it !