Formulas for Oscillations
From the calculus, we can solve -kx = ma
(this is a differential equation) -kx = m d2x/dt2
to get: x = A sin(wt + qo) where w = [k/m]1/2.
This should appear reasonable: the sine function oscillates (goes up and down in value) just like the mass oscillates! But the sine function needs an angle to operate on! Where is the angle in the problem?