Transform to normal form and solve: Uxy = Uxx a. u= f (y) + f2(x -y) b. u = f (y ) + f 2 (x + y ) c. u=f(y ) + f 2(y - x) d. u= f ( x) + f 2(x -y) e. u= f ( x) + f2(x+ y). Oa.