Let A be a matrix and [1, 2; 0, 1] A [2, 0; -1, 1] = [1, 0; 0, 1]. If |A| and |A^2| are the roots of the quadratic equation a x^2+b x+3=0, then a+b-a…

Let $\displaystyle A$ be a matrix and $\displaystyle \left[\begin{array}{ll}1 & 2 \\ 0 & 1\end{array}\right] A\left[\begin{array}{cc}2 & 0 \\ -1 & 1\end{array}\right]=\left[\begin{array}{cc}1 & 0 \\ 0 & 1\end{array}\right]$. If $\displaystyle |A|$ and $\displaystyle \left|A^2\right|$ are the roots of the quadratic equation $\displaystyle a x^2+b x+3=0$, then $\displaystyle a+b-a b$ is equal to