# Joint Probability Distribution and covariance

If $$f(x,y)=1/4$$ $$x=-3,y=-5; x=-1,y=-1; x=1,y=1; x=3,y=5.$$Find cov (x,y).

I know the formula for cov (X,Y) but I'm stuck at finding E (x) and E (y).

• Use the definition of expectation. – whuber Feb 4 at 16:52
• @whuber Is E (x)=0= E (y)? – Jor_El Feb 4 at 16:55
• Please use the [self-study] tag. – Tim Feb 4 at 16:56
• To apply the definition to $x,$ make a table of all the values of $x$ and their probabilities, then sum the products of the values and their probabilities. – whuber Feb 4 at 17:00
• @whuber does each x have same probability i.e equal to 1/4? – Jor_El Feb 4 at 17:04