If $\left[ {\begin{array}{*{20}{c}}2&{ – 3}\\4&0\end{array}} \right] – \left[ {\begin{array}{*{20}{c}}a&c\\b&d\end{array}} \right] = \left[ {\begin{array}{*{20}{c}}1&4\\2&{ – 5}\end{array}} \right]$, then $(a,b,c,d) = $

If $A\, = \,\left[ {\begin{array}{*{20}{c}}
0&{ – 1}\\
1&0
\end{array}} \right],$ then which one of the following statements is not correct?

Let $A$ and $B$ be any two $n \times n$ matrices such that the following conditions hold: $A B=B A$ and there exist positive integers $k$ and $l$ such that $A^k=I$ ( the identity matrix) and $B^l=0$ (the zero matrix). Then,

$A = \left[ {\begin{array}{*{20}{c}}5&{ – 3}\\2&4\end{array}} \right]$and $B = \left[ {\begin{array}{*{20}{c}}6&{ – 4}\\3&6\end{array}} \right],$ then $A – B = $

If $A=\left[\begin{array}{lll}1 & 1 & 1 \\ 0 & 1 & 1 \\ 0 & 0 & 1\end{array}\right]$ and $M=A+A^{2}+A^{3}+\ldots .+A^{20}$, then the sum of all the elements of the matrix $\mathrm{M}$ is equal to $…..$