The displacement of a wave on a string is given by
y=0.04cos(6x−150t),
where x is in metres and t in seconds. Which of the following represents a wave with the same amplitude, wavelength and frequency but travelling in the opposite direction?
a) y=0.04cos(−6x+150t)
b) y=0.04cos(6x+150t)
c) −0.04cos(6x−150t)
d) y=0.04cos(6x−75t)