Question
If \[A = \left[ {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right],\] then $$A^{16}$$ is equal to :
A.
\[\left[ {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right]\]
B.
\[\left[ {\begin{array}{*{20}{c}}
0&{1}\\
1&0
\end{array}} \right]\]
C.
\[\left[ {\begin{array}{*{20}{c}}
{ - 1}&0\\
0&1
\end{array}} \right]\]
D.
\[\left[ {\begin{array}{*{20}{c}}
1&{ 0}\\
0&1
\end{array}} \right]\]
Answer :
\[\left[ {\begin{array}{*{20}{c}}
1&{ 0}\\
0&1
\end{array}} \right]\]
Solution :
\[\begin{array}{l}
{\rm{We \,\,have, }}\,\,A = \left[ {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right]\\
{\rm{Now, }}\,\,{A^2} = A.A = \left( {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right)\left( {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right) = \left( {\begin{array}{*{20}{c}}
{ - 1}&0\\
0&{ - 1}
\end{array}} \right) = - I\\
{\rm{where }}\,\,I = \left( {\begin{array}{*{20}{c}}
1&0\\
0&1
\end{array}} \right){\rm{ is\,\, identity\,\, matrix}}
\end{array}\]
$$\eqalign{
& {\left( {{A^2}} \right)^8} = {\left( { - I} \right)^8} = I. \cr
& {\text{Hence, }}{A^{16}} = I \cr} $$