若Y=a+bX,则有:
令E(X) = μ,D(X) = σ
则E(Y) = bμ + a,D(Y) = bσ
E(XY) = E(aX + bX) = aμ + b(σ + μ)
Cov(X,Y) = E(XY) − E(X)E(Y) = bσ