Respuesta :
We are given the following matrix:
[tex]A=\begin{bmatrix}{4} & {-7} & {} \\ {-2} & {1} & {} \\ {} & {} & {}\end{bmatrix}[/tex]We are asked to determine the coefficients of:
[tex]A^{-1}[/tex]Which is the inverse matrix. To do that let's remember that the inverse of a 2 by 2 matrix of the form:
[tex]A=\begin{bmatrix}{a_1} & {a_2} & {} \\ {a_3} & {a_4} & {} \\ {} & {} & {}\end{bmatrix}[/tex]is:
[tex]A^{-1}=\frac{1}{\det A}\begin{bmatrix}{a_4} & {-a_2} & {} \\ {-a_3} & {a_1} & {} \\ {} & {} & {}\end{bmatrix}[/tex]The value of the determinant of A (det A) is given by:
[tex]\det A=a_1a_4-a_2a_3[/tex]Replacing we get:
[tex]A^{-1}=\frac{1}{a_1a_4-a_2a_3}\begin{bmatrix}{a_4} & {-a_2} & {} \\ {-a_3} & {a_1} & {} \\ {} & {} & {}\end{bmatrix}[/tex]Replacing the values:
[tex]A^{-1}=\frac{1}{(4)(1)-(-7)(-2)}\begin{bmatrix}{1_{}} & {7_{}} & {} \\ {2_{}} & {4_{}} & {} \\ {} & {} & {}\end{bmatrix}[/tex]Solving the operations:
[tex]A^{-1}=-\frac{1}{10}\begin{bmatrix}{1_{}} & {7_{}} & {} \\ {2_{}} & {4_{}} & {} \\ {} & {} & {}\end{bmatrix}[/tex]Or:
[tex]A^{-1}=\begin{bmatrix}{-\frac{1}{10}_{}} & {-\frac{7}{10}_{}} & {} \\ -{\frac{1}{5}_{}} & {-\frac{2}{5}_{}} & {} \\ {} & {} & {}\end{bmatrix}[/tex]Therefore, we have:
[tex]\begin{gathered} a=-\frac{1}{10} \\ b=-\frac{7}{10} \\ c=-\frac{1}{5} \\ d=-\frac{2}{5} \end{gathered}[/tex]