Finding the equation of motion from amplitude and phase angle

[Alexan]

$T = \frac{2\pi}{\omega}$

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[PeroK]

?

I assume that your book has a description and analysis of simple harmonic motion. I think you need to re-read that section.

If not, try:

https://www.khanacademy.org/science...introduction-to-simple-harmonic-motion-review