Practicing Success
If $A=\left[\begin{array}{rr}2 & 3 \\ 5 & -2\end{array}\right]$ then : |
$A^{-1}=\frac{1}{11} A$ $A^{-1}=\frac{1}{19} A$ $A^{-1}=-\frac{1}{19} A$ $A^{-1}=\frac{1}{7} A$ |
$A^{-1}=\frac{1}{19} A$ |
$A=\left[\begin{array}{cc}2 & 3 \\ 5 & -2\end{array}\right]$ finding cofactors of A C11 = -2 C12 = -5 C21 = -3 C22 = 2 so Adj A = $\left[\begin{array}{ll}C_{11} & C_{12} \\ C_{21} & C_{22}\end{array}\right]^{T}=\left[\begin{array}{cc}-2 & -5 \\ -3 & 2\end{array}\right]^{T}=\left[\begin{array}{cc}-2 & -3 \\ -5 & 2\end{array}\right]$ = Adj A |A| = 2(-2) - 5(3) = -4 - 15 = -19 so $A^{-1}=\frac{1}{|A|} adj~A=\frac{-1}{19}\left[\begin{array}{ll}-2 & -3 \\ -5 & 2\end{array}\right]$ $\Rightarrow \frac{1}{19}\left[\begin{array}{rr}2 & 3\\ 5 & -2\end{array}\right]$ |