Let X1,X2X_1, X_2X1,X2 be i.i.d. N(0,1)N(0, 1)N(0,1). Find E[X12+2X1X2+X22]E[X_1^2 + 2X_1X_2 + X_2^2]E[X12+2X1X2+X22].
1
2
0
4