# Basic SHM 2

Which equation is known as the Hallmark of SHM?

1. $$\dfrac{d^2 x}{dt^2} + x\omega^2 = 0$$.

2. $$a(t) = -\omega^2 A \sin(\omega t + \phi)$$.

3. $$\dfrac{v^2}{\omega^2 A^2} + \dfrac{x^2}{A^2} = 1$$.

4. $$x = A \sin(\omega t) + \phi$$.

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