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).

  • $\begingroup$ Use the definition of expectation. $\endgroup$ – whuber Feb 4 at 16:52
  • $\begingroup$ @whuber Is E (x)=0= E (y)? $\endgroup$ – Jor_El Feb 4 at 16:55
  • $\begingroup$ Please use the [self-study] tag. $\endgroup$ – Tim Feb 4 at 16:56
  • $\begingroup$ 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. $\endgroup$ – whuber Feb 4 at 17:00
  • $\begingroup$ @whuber does each x have same probability i.e equal to 1/4? $\endgroup$ – Jor_El Feb 4 at 17:04

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