If all the elements of 3× 3 matrix A are 1 , then A^2-3A is

$A=\begin{bmatrix}1&1&1\\1&1&1\\1&1&1\end{bmatrix}$

$A^2=\begin{bmatrix}3&3&3\\3&3&3\\3&3&3\end{bmatrix}$

so $A^2=3A$

$⇒A^2-3A=0$