Given that \( A=\left(\begin{array}{lll}2 & 3 & 5 \\ 4 & 1 & 6 \\ 1 & 4 & 0\end{array}\right) \), find the inverse of \( A \)
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Bonus Knowledge
To find the inverse of the matrix \( A = \begin{pmatrix} 2 & 3 & 5 \\ 4 & 1 & 6 \\ 1 & 4 & 0 \end{pmatrix} \), we can use the formula for the inverse of a \( 3 \times 3 \) matrix. This involves calculating the determinant of \( A \) and the matrix of minors, cofactors, and adjugate. 1. **Calculate the determinant of \( A \):** \[ \text{det}(A) = 2 \begin{vmatrix} 1 & 6 \\ 4 & 0 \end{vmatrix} - 3 \begin{vmatrix} 4 & 6 \\ 1 & 0 \end{vmatrix} + 5 \begin{vmatrix} 4 & 1 \\ 1 & 4 \end{vmatrix} \] Calculating the \( 2 \times 2 \) determinants: - \(\begin{vmatrix} 1 & 6 \\ 4 & 0 \end{vmatrix} = (1)(0) - (6)(4) = -24\) - \(\begin{vmatrix} 4 & 6 \\ 1 & 0 \end{vmatrix} = (4)(0) - (6)(1) = -6\) - \(\begin{vmatrix} 4 & 1 \\ 1 & 4 \end{vmatrix} = (4)(4) - (1)(1) = 16 - 1 = 15\) Putting it all together: \[ \text{det}(A) = 2(-24) - 3(-6) + 5(15) = -48 + 18 + 75 = 45 \] 2. **Find the matrix of minors, cofactors, and adjugate:** The minors are computed as follows: - Minor \( M_{11} = -24 \) - Minor \( M_{12} = -6 \) - Minor \( M_{13} = 15 \) - Minor \( M_{21} = -30 \) - Minor \( M_{22} = -10 \) - Minor \( M_{23} = 22 \) - Minor \( M_{31} = 18 \) - Minor \( M_{32} = -12 \) - Minor \( M_{33} = -6 \) The cofactors take into account the checkerboard pattern of signs: \[ \text{Cofactor Matrix} = \begin{pmatrix} -24 & 6 & 15 \\ 30 & -10 & -22 \\ 18 & 12 & -6 \end{pmatrix} \] Next, we take the transpose to find the adjugate: \[ \text{Adj}(A) = \begin{pmatrix} -24 & 30 & 18 \\ 6 & -10 & 12 \\ 15 & -22 & -6 \end{pmatrix} \] 3. **Calculate the inverse:** \[ A^{-1} = \frac{1}{\text{det}(A)} \cdot \text{Adj}(A) = \frac{1}{45} \begin{pmatrix} -24 & 30 & 18 \\ 6 & -10 & 12 \\ 15 & -22 & -6 \end{pmatrix} \] Thus, the inverse of \( A \) can be expressed as: \[ A^{-1} = \begin{pmatrix} -\frac{24}{45} & \frac{30}{45} & \frac{18}{45} \\ \frac{6}{45} & -\frac{10}{45} & \frac{12}{45} \\ \frac{15}{45} & -\frac{22}{45} & -\frac{6}{45} \end{pmatrix} \] This simplifies to: \[ A^{-1} = \begin{pmatrix} -\frac{8}{15} & \frac{2}{3} & \frac{2}{5} \\ \frac{2}{15} & -\frac{2}{9} & \frac{4}{15} \\ \frac{1}{3} & -\frac{22}{45} & -\frac{2}{15} \end{pmatrix} \]