The distance between the first and the third nodes of a standing wave is 0.2 m, its maximum displacement is 0.02 m and its frequency is 40 Hz. The wave- functions of the two travelling waves which interfere to give the standing wave are then: y1 = 0.01 sin(10x-80nt); y2 0.01 sin(10tx+80rt), y1 = 0.01 sin(5rx-40nt); y2 0.01 sin(5rx+40nt), y1 = 0.04 sin(20tx-320nt); y2 = 0.04 sin(20rtx+320nt), y1 = 0.005 sin(5nx-40nt); y2 = 0.005 sin(5rx+40nt), y1 = 0.02 sin(20nx-320nt); y2 = 0.02 sin(20rx+320nt),