- Home
- Standard 12
- Mathematics
For the matrix $A = \left[ {\begin{array}{*{20}{c}}1&1&0\\1&2&1\\2&1&0\end{array}} \right]$, which of the following is correct
${A^3} + 3{A^2} - I = O$
${A^3} - 3{A^2} - I = O$
${A^3} + 2{A^2} - I = O$
${A^3} - {A^2} + I = O$
Solution
(b) ${A^2} = AA = \left[ {\,\begin{array}{*{20}{c}}1&1&0\\1&2&1\\2&1&0\end{array}\,} \right]\,\left[ {\,\begin{array}{*{20}{c}}1&1&0\\1&2&1\\2&1&0\end{array}\,} \right]$= $\left[ {\,\begin{array}{*{20}{c}}2&3&1\\5&6&2\\3&4&1\end{array}\,} \right]$
==>${A^3} = {A^2}A = \left[ {\,\begin{array}{*{20}{c}}2&3&1\\5&6&2\\3&4&1\end{array}\,} \right]\,\,\left[ {\,\begin{array}{*{20}{c}}1&1&0\\1&2&1\\2&1&0\end{array}\,} \right]$=$\left[ {\,\begin{array}{*{20}{c}}7&9&3\\{15}&{19}&6\\9&{12}&4\end{array}\,} \right]$
Here,${A^3} – 3{A^2} = \left[ {\,\begin{array}{*{20}{c}}1&0&0\\0&1&0\\0&0&1\end{array}\,} \right]\, = I $ ==> ${A^3} – 3{A^2} – I = 0$.