Write the expression for the wavefunction of a harmonic wave of amplitude A, period T, and speed v, propagating in the negative x-direction.
a) A * sin(2π/T * t - 2πx/T)
b) A * cos(2π/T * t + 2πx/T)
c) A * sin(2π/T * t + 2πx/T)
d) A * cos(2π/T * t - 2πx/T)
