For each of the following functions f: R → R, determine whether f is invertible, and, if so, determine f-1.
(a) f = {(x, y)|2x + 3y = 7}
(b) f = {(x, y)\ax + by = c,b f 0}
(c) f = {(x,y)\y =x3}
(d) f = {(x, y)|y = x4 + x}