The general expression for speed is speed=distance/time.The wavelength (lambda) of a wave is the distance between one point on an oscillation to the exact same point on the next oscillation, or more simply the distance travelled in one oscillation. The time period (T) of a wave is the time taken for one complete oscillation. Therefore, for one oscillation, the distance travelled is the wavelength (Lambda) and the time taken is the time period (T). Using the general equation for speed, this gives wave speed (v)=wavelength (Lambda)/Time Period (T).The frequency (f) of a wave is the number of oscillations that occur in one second, and has a relationship with the time period (T) of frequency (f)=1/time period (T). Substituting this into the equation for wave speed gives wave speed (v)=frequency (f) x wavelength (Lambda).