## College Algebra (6th Edition)

If $A=\left[\begin{array}{ll} a & b\\ c & d \end{array}\right]$, then $A^{-1}=\displaystyle \frac{1}{ad-bc}\left[\begin{array}{ll} d & -b\\ -c & a \end{array}\right]$. The matrix $A$ is invertible if and only if $ad-bc\neq 0$. -------------------- $ad-bc=6(1)-(-3)(-2)=6-6=0$ so, A does not have an inverse.