1. For the following functions f(:c, t), which one are waves? For the ones that are waves, write down the speed of the wave and whether the wave is moving leftward or rightward. (10 points) (a) f(:t:, t) = 10exp(30:r - 159) (h) f (2:, t) = -3 cos(2:1:2 - 4t2) (c) [(22, t) = 10\\/:r+t (d) [(z, t) = 10 tan(:r + t) exp(a: - t)