>>643
E(X^2) =∫[-∞,∞] x＾2*k*exp(-λ|x|)dx
= 2k*∫[0,∞] x＾2*exp(-λx)dx
= λ*(1/λ^3)*∫[0,∞] x＾2*exp(-x)dx
= 2/λ^2