1. For the following functions f(, 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(x, t) - 4tan(x - 3t) (b) f(x, t) - 20 exp[10(3: + 20)] (c) f(x, t) - 10 exp[-(6x + 3t)21 (d) f(x, t) - cos( 10.2 -513)