If $\left(a\sec \theta ,b\tan \theta \right)$ and $\left(a\sec \varphi ,b\tan \varphi \right)$ be two coordinate of the ends of a focal chord passing through $\left(ae,0\right)$ of $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$ then $\tan \left(\frac{\theta }{2}\right)\tan \left(\frac{\varphi }{2}\right)$ equals to

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