Practicing Success
The inverse of the matrix $A=\begin{bmatrix} a & b\\c & \frac{1+bc}{a}\end{bmatrix}$ is : |
$\begin{bmatrix} -a & c\\b & \frac{-1-bc}{a}\end{bmatrix}$ $\begin{bmatrix} \frac{1+bc}{a} & -b\\-c & a\end{bmatrix}$ $\begin{bmatrix} c & \frac{1+bc}{a}\\a &b\end{bmatrix}$ $\begin{bmatrix} \frac{1+bc}{a} & -c\\-b & a\end{bmatrix}$ |
$\begin{bmatrix} \frac{1+bc}{a} & -b\\-c & a\end{bmatrix}$ |
The correct answer is Option (2) → $\begin{bmatrix} \frac{1+bc}{a} & -b\\-c & a\end{bmatrix}$ $A=\begin{bmatrix} a & b\\c & \frac{1+bc}{a}\end{bmatrix}$ $|A|=1+bc-bc=1$ finding cofactors $c_{11}=\frac{1+bc}{a}, c_{12}=-c$ $c_{21}=-b,c_{22}=a$ so $Adj\,A=\begin{bmatrix} c_{11} & c_{12}\\c_{21} & c_{22}\end{bmatrix}^T$ $Adj\,A=\begin{bmatrix} \frac{1+bc}{a} & -b\\-c & a\end{bmatrix}$ $A^{-1}=\frac{Adj\,A}{|A|}=\begin{bmatrix} \frac{1+bc}{a} & -b\\-c & a\end{bmatrix}$ |