5l
The waves emanating from S1 will arrive exactly two and a half cycles
later than the waves from S2  [Fig 10 10(b)] Thus if the displacement
produced by  S1  is given by
y1 = a cos wt
then the displacement produced by  S2  will be given by
y2 = a cos (wt + 5p)  = – a cos wt
FIGURE 10