Proving differential equation has no bounded solutions

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How do I prove that the $2^{nd}$ order ODE

$$\ddot{x}(t) - \sin(x(t)) = \sin(t)$$

has no solutions $~\{x(0),\dot{x}(0)\} \in \mathbb{R}^2~$ for which $|x(t)| < \frac{\pi}{2} \quad \forall \ t\in[0,\infty]~$?