Finding the expression for a polarized light wave

1. The problem statement, all variables and given/known data

Find an expression for the P-state lightwave of angular frequency w and amplitude E_0 propagating along a line in the xy-plane at 45 degrees to the x-axis and having its plane of vibration corresponding to the xy-plane. At t = 0, y = 0, and x = 0 the field is 0.

2. Relevant equations

E_0x = E_0 cos(45)
E_0y = E_0 sin(45)

3. The attempt at a solution

I thought that it would be a sine wave given the initial conditions
Thus, E = (-i + j) sqrt(2)/2 E_0 sin(k/sqrt(2) (x + y) - wt)

where k = k(i + j)/sqrt(2)

Or is it going to be a cosine wave?