$y = \frac{1}{{\sqrt a }}\,\sin \,\omega t \pm \frac{1}{{\sqrt b }}\,\cos \,\omega t$ will be
$y=\sqrt{\left(\frac{1}{\sqrt{a}}\right)^{2}+\left(\frac{1}{\sqrt{b}}\right) \sin (\omega t+\phi)}$
$\mathrm{y}=\left(\frac{1}{\mathrm{a}}+\frac{1}{\mathrm{b}}\right) \sin (\omega \mathrm{t}+\phi)$
amplitude $A=\sqrt{\frac{1}{a}+\frac{1}{b}}=\sqrt{\frac{a+b}{a b}}$
