Matrix and Determinant
78813
If matrix \(A=\left[\begin{array}{ll}1 & 2 \\ 4 & 3\end{array}\right]\), such that, \(A X=I\) then \(\mathrm{X}=\) \(\qquad\)
1 \(\overline{\frac{1}{5}}\left[\begin{array}{cc}1 & 3 \\ 2 & -1\end{array}\right]\)
2 \(\frac{1}{5}\left[\begin{array}{cc}4 & 2 \\ 4 & -1\end{array}\right]\)
3 \(\frac{1}{5}\left[\begin{array}{cc}-3 & 2 \\ 4 & -1\end{array}\right]\)
4 \(\frac{1}{5}\left[\begin{array}{ll}-1 & 2 \\ -1 & 4\end{array}\right]\)
Explanation:
(C) : Given that,
\(\mathrm{A}=\left[\begin{array}{ll}1 & 2 \\ 4 & 3\end{array}\right]\)
Now, \(\mathrm{AX}=\mathrm{I}\)
On multiplying \(\mathrm{A}^{-1}\) on both side, we get -
\(\mathrm{A}^{-1} \mathrm{AX}=\mathrm{A}^{-1} \mathrm{I}\)
\(\mathrm{IX}=\mathrm{A}^{-1}\)
We have,
\(\mathrm{A}=\left[\begin{array}{ll}1 & 2 \\ 4 & 3\end{array}\right]\)
\(|\mathrm{A}|=3-8=-5 \quad\left(\begin{array}{l}\text { We know that } \\ \mathrm{A}^{-1}=\frac{\text { AdjA }}{|\mathrm{A}|}\end{array}\right)\)
And \(\quad \operatorname{adj} A=\left[\begin{array}{cc}3 & -2 \\ -4 & 1\end{array}\right]\)
\(\therefore \quad \mathrm{X}=\mathrm{A}^{-1}\)
\(\mathrm{A}^{-1}=\mathrm{X}=-\frac{1}{5}\left[\begin{array}{cc}3 & -2 \\ -4 & 1\end{array}\right]\)
\(X=\frac{1}{5}\left[\begin{array}{cc}-3 & 2 \\ 4 & -1\end{array}\right]\)