\(y(x, t)=e^{-\left(a x^2+b t^2+2 \sqrt{a b} x t\right)}=e^{-(\sqrt{a} x+\sqrt{b} t)^2}\)
It is a function of type
\(y=f(\omega t+k x)\)
\(\therefore y(x, t)\) represents wave travelling along
\(-x\) direction.
Speed of wave \(=\frac{\omega}{k}=\frac{\sqrt{b}}{\sqrt{a}}=\sqrt{\frac{b}{a}}\).