Trinomial Identity

$\begin{displaymath} (x^2+axy+by^2)(t^2+atu+bu^2)=r^2+ars+bs^2, \end{displaymath}$

(1)

where

$\displaystyle r$	$\textstyle =$	$\displaystyle xt-byu$	(2)
$\displaystyle s$	$\textstyle =$	$\displaystyle yt+xu+ayu.$	(3)