Out of the following functions representing motion of a particle...

For a simple harmonic motion $$\frac{d^2 y}{d t^2} \propto-y$$ Hence, equation $y=\sin \omega t-\cos \omega t and$y=5 \cos $\left(\frac{3 \pi}{4}-3 \omega t\right)$ are satisfying this condition and equation $y=1+\omega t+\omega^2 t^2$ is not periodic and $y=\sin ^3 \omega t$ is periodic but not SHM. Option (3) is correct