[Standing waves] The vibrations of a string fixed at both ends are represented by y = 16 sin(πx/15) 

[Standing waves] The vibrations of a string fixed at both ends are represented by y = 16 sin(πx/15) cos(96πt) where x and y are in cm and t in seconds. Then the phase difference between the points at x =13 cm and x = 16 cm in radian is
1) π/5
2) π
3) 0
4) 2π/5