$\frac{1}{2} m \omega^{2} A^{2}+\frac{1}{2} m \omega^{2} A^{2}=m \omega^{2} A^{2}$
Let $A^{\prime}$ be the new amplitude. (apply energy conservation law)
$\frac{1}{2} m_{\omega}^{2}\left(A^{\prime}\right)=m_{\omega}^{2} A^{2}$
${A}^{\prime}=\sqrt{2} A$




$x = 3\,sin\, 20\pi t + 4\, cos\, 20\pi t$ ,
where $x$ is in $cms$ and $t$ is in $seconds$ . The amplitude is ..... $cm$