To calculate the transverse wave speed from the given wave function, focus on the relationship between displacement and time. The wave function provided is 15.0 cm cos(πx - 15πt), indicating that the wave speed is constant and does not depend on position. To find the transverse speed at a specific displacement of 12.0 cm, differentiate the wave function with respect to time, yielding the rate of change dy/dt. This approach simplifies the problem by eliminating the x-variable, allowing for a direct calculation of the transverse speed at the specified displacement. Understanding this relationship is key to solving the problem accurately.