a) Write out an expression in powers of (x +1) and (y - 1) for f(x, y) = x2 + xy + y2.
b) Write Taylor's Formula for f(x, y) = √x + √y, a = (1, 4), and p = 3.
c) Write Taylor's Formula for f(x, y) = exy, a = (0, 0), and p = 4.