So matrix A is
1 2 1 0
3 1 2 3
2 5 0 1
2 -1 1 3
how will i go able showing that this matrix ISNT invertible?
A square matrix $\displaystyle \displaystyle \begin{align*} \mathbf{A} \end{align*}$ is only invertible if $\displaystyle \displaystyle \begin{align*} |\mathbf{A}| \neq 0 \end{align*}$, so to show that this matrix is NOT invertible, evaluate $\displaystyle \displaystyle \begin{align*} |\mathbf{A}| \end{align*}$ and show that it equals 0.
double post
Show that a matrix ISNT invertible?