5. Tind the inverse of the matrix \( A=\left[\begin{array}{ccc}4 & -2 & 1 \\ 7 & 3 & 3 \\ 2 & 0 & 1\end{array}\right] \)
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To find the inverse of the matrix \( A=\left[\begin{array}{ccc}4 & -2 & 1 \\ 7 & 3 & 3 \\ 2 & 0 & 1\end{array}\right] \), we can use the formula \( A^{-1} = \frac{1}{\text{det}(A)} \text{adj}(A) \). First, we need to calculate the determinant of matrix \( A \): \[ \text{det}(A) = 4(3 \cdot 1 - 3 \cdot 0) - (-2)(7 \cdot 1 - 3 \cdot 2) + 1(7 \cdot 0 - 3 \cdot 2) = 4(3) + 2(1) - 6 = 12 + 2 - 6 = 8. \] Next, we can compute the adjugate of \( A \) by finding the cofactor matrix and then transposing it. 1. Calculate the cofactor for each element: - \( C_{11} = \text{det}\left(\begin{array}{cc}3 & 3 \\ 0 & 1\end{array}\right) = 3 \) - \( C_{12} = -\text{det}\left(\begin{array}{cc}7 & 3 \\ 2 & 1\end{array}\right) = - (7 \cdot 1 - 3 \cdot 2) = - (7 - 6) = -1 \) - \( C_{13} = \text{det}\left(\begin{array}{cc}7 & 3 \\ 2 & 0\end{array}\right) = 7 \cdot 0 - 3 \cdot 2 = -6 \) - \( C_{21} = -\text{det}\left(\begin{array}{cc}-2 & 1 \\ 0 & 1\end{array}\right) = -(-2 \cdot 1 - 1 \cdot 0) = 2 \) - \( C_{22} = \text{det}\left(\begin{array}{cc}4 & 1 \\ 2 & 1\end{array}\right) = 4 \cdot 1 - 1 \cdot 2 = 2 \) - \( C_{23} = -\text{det}\left(\begin{array}{cc}4 & -2 \\ 2 & 0\end{array}\right) = -(4 \cdot 0 - (-2) \cdot 2) = -4 \) - \( C_{31} = \text{det}\left(\begin{array}{cc}-2 & 1 \\ 3 & 3\end{array}\right) = -2\cdot3 - 1\cdot3 = -6 \) - \( C_{32} = -\text{det}\left(\begin{array}{cc}4 & 1 \\ 7 & 3\end{array}\right) = -(4 \cdot 3 - 1 \cdot 7) = -(12 - 7) = -5 \) - \( C_{33} = \text{det}\left(\begin{array}{cc}4 & -2 \\ 7 & 3\end{array}\right) = 4 \cdot 3 - (-2) \cdot 7 = 12 + 14 = 26 \) The cofactor matrix is: \[ \text{Cof}(A) = \left[\begin{array}{ccc} 3 & -1 & -6 \\ 2 & 2 & -4 \\ -6 & -5 & 26 \end{array}\right]. \] Now taking the transpose to find the adjugate: \[ \text{adj}(A) = \left[\begin{array}{ccc} 3 & 2 & -6 \\ -1 & 2 & -5 \\ -6 & -4 & 26 \end{array}\right]. \] Finally, we can find the inverse: \[ A^{-1} = \frac{1}{8} \left[\begin{array}{ccc} 3 & 2 & -6 \\ -1 & 2 & -5 \\ -6 & -4 & 26 \end{array}\right] = \left[\begin{array}{ccc} \frac{3}{8} & \frac{1}{4} & -\frac{3}{4
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