For the following pairs of sinusoids, determine which one leads and by how much.
(a) v(t) = 10 cos(4t - 60o) and i(t) = 4 sin (4t + 50o)
(b) v1 (t) = 4 cos(377t + 10o) and v2 (t) = -20 cos 377t
(c) x(t) = 13 cos 2t + 5 sin 2t and y(t) = 15 cos(2t -11.8o)