(b)(iii) Sketch the standing wave at t = (3/15)T

y = -8 cos3p t sin6p x

[Remember from Q1 that T = 2/3 s]

at t = (3/15)T = (3/15)(2/3) = 2/15 s

y = -8 cos3p (2/15) sin6p x

= -8 cos0.4p sin6p x

= -8 cos 72° sin 6p x

= -2.47 sin 6p x

This is just a negative sine curve with a maximum of 2.47 and a wave length of 1/3

(Remember k = 6p = 2p /l)