If X1, X2, X3, and X4 are (pairwise) uncorrelated random variables, each having mean - 1 and variance 1, compute the correlations of (a) X+X2 and X2 + X3 (b) X1 +X2 and X3 +X4 = (a) p(x1+X2X2+X3) = (Type an exact answer in simplified form.)