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I'm looking for the E[XY] of the joint moment generating function of a couple of random variables (X,Y). We don't know if the variables are independent. I don't know how to solve the partial derivative ∂² E[e^(sX+tY)] ∂s ∂t

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  • $\begingroup$ What information do you have about the variables? $\endgroup$ – Graham Kemp Feb 3 '17 at 2:18
  • $\begingroup$ I don't have any information, I think I need to find a general equation for the (X,Y) couple $\endgroup$ – h1gh5ive Feb 3 '17 at 2:36
  • $\begingroup$ Do we at least know if continuous of discrete they are? $\endgroup$ – Graham Kemp Feb 3 '17 at 3:00
  • $\begingroup$ I suppose they are continuous $\endgroup$ – h1gh5ive Feb 3 '17 at 3:01

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