On the homeostasis expression of alternating current When to use EM = coswt, when to use EM = sinwt?

On the homeostasis expression of alternating current When to use EM = coswt, when to use EM = sinwt?

Look at where the coil is at the beginning
If the coil is initially parallel to the magnetic field, then
E=nBSwcoswt
If the coil is perpendicular to the magnetic field at the beginning, then
E=nBSwsinwt