please help me with both questions.

(c) Suppose that u and v are parallel vectors that point in the opposite direction. That is, v = -au for some positive real number a. Using the fact that laul = alul , prove that the angle 0 between the vectors satisfies the standard formula: u . v cos(0) = (d) Let m = ai + bj, n = bi + aj, and the angle between two vectors be 0. Prove the following result