1. The problem statement, all variables and given/known data Suppose you send an incident wave of specified shape, g_I(z - v_1 * t ) , down string number 1. It gives rise to a reflected wave, h_R(z + v_1 *t ) , and a transmitted wave, g_T(z - v_2 *t). By imposing the boundary conditions, find h_R and g_T. 2. Relevant equations I know that the boundary conditions are such that the first derivative and second derivative of the sum of the waves on one side is equal to the of the other side. 3. The attempt at a solution I know that from boundary condition 1, gI(-v_1 *t) + h_R(v_1 *t) = g_T(-v_2 *t). How do I proceed from this? The hint given is that dg_I/dz = (-1/v_1)*(dg_I / dt). I've tried chain rule with that but I can't get the minus sign.