Find Variance of random variable $X=2Y-3Z$. Given that $EY=0,EZ=2,VarX=2,VarZ=1,p(Y,Z)=\frac{-1}{\sqrt2},EX=6$.
Knowing that $Var(X)=Var(2Y)+Var(-3Z)+2(E(-6YZ)-E(2Y)E(-3Z)).$ Remains only to find $E(YZ)$. This is where I am stuck now. $E(YZ)=\sum_{(yz)} yzp(y,z)$ I am not sure what are values for $y,z$ in this case.