Question #287797

find the inverse of this matrix


A= 1 3 5 4


7 2 9 6


1
Expert's answer
2022-01-18T10:42:53-0500
A=[135472968]A=\begin{bmatrix} 1 & 3 & 5 \\ 4 & 7 & 2 \\ 9 & 6 & 8 \end{bmatrix}

[135100472010968001]\begin{bmatrix} 1 & 3 & 5 & & 1 & 0 & 0 \\ 4 & 7 & 2 & & 0 & 1 & 0 \\ 9 & 6 & 8 & & 0 & 0 & 1 \end{bmatrix}

R2=R24R1R_2=R_2-4R_1


[1351000518410968001]\begin{bmatrix} 1 & 3 & 5 & & 1 & 0 & 0 \\ 0 & -5 & -18 & & -4 & 1 & 0 \\ 9 & 6 & 8 & & 0 & 0 & 1 \end{bmatrix}

R3=R39R1R_3=R_3-9R_1


[135100051841002137901]\begin{bmatrix} 1 & 3 & 5 & & 1 & 0 & 0 \\ 0 & -5 & -18 & & -4 & 1 & 0 \\ 0 & -21 & -37 & & -9 & 0 & 1 \end{bmatrix}

R2=R2/5R_2=-R_2/5


[1351000118/54/51/5002137901]\begin{bmatrix} 1 & 3 & 5 & & 1 & 0 & 0 \\ 0 & 1 & 18/5 & & 4/5 & -1/5 & 0 \\ 0 & -21 & -37 & & -9 & 0 & 1 \end{bmatrix}

R1=R13R2R_1=R_1-3R_2


[1029/57/53/500118/54/51/5002137901]\begin{bmatrix} 1 & 0 & -29/5 & & -7/5 & 3/5 & 0 \\ 0 & 1 & 18/5 & & 4/5 & -1/5 & 0 \\ 0 & -21 & -37 & & -9 & 0 & 1 \end{bmatrix}

R3=R3+21R2R_3=R_3+21R_2


[1029/57/53/500118/54/51/5000193/539/521/51]\begin{bmatrix} 1 & 0 & -29/5 & & -7/5 & 3/5 & 0 \\ 0 & 1 & 18/5 & & 4/5 & -1/5 & 0 \\ 0 & 0 & 193/5 & & 39/5 & -21/5 & 1 \end{bmatrix}

R3=5R3/193R_3=5R_3/193


[1029/57/53/500118/54/51/5000139/19321/1935/193]\begin{bmatrix} 1 & 0 & -29/5 & & -7/5 & 3/5 & 0 \\ 0 & 1 & 18/5 & & 4/5 & -1/5 & 0 \\ 0 & 0 & 1 & & 39/193 & -21/193 & 5/193 \end{bmatrix}

R1=R1+29R3/5R_1=R_1+29R_3/5


[10044/1936/19329/1930118/54/51/5000139/19321/1935/193]\begin{bmatrix} 1 & 0 & 0 & & -44/193 & -6/193 & 29/193 \\ 0 & 1 & 18/5 & & 4/5 & -1/5 & 0 \\ 0 & 0 & 1 & & 39/193 & -21/193 & 5/193 \end{bmatrix}

R2=R218R3/5R_2=R_2-18R_3/5


[10044/1936/19329/19301014/19337/19318/19300139/19321/1935/193]\begin{bmatrix} 1 & 0 & 0 & & -44/193 & -6/193 & 29/193 \\ 0 & 1 & 0 & & 14/193 & 37/193 & -18/193 \\ 0 & 0 & 1 & & 39/193 & -21/193 & 5/193 \end{bmatrix}

We are done. On the left is the identity matrix. On the right is the inverse matrix.


A1=[44/1936/19329/19314/19337/19318/19339/19321/1935/193]A^{-1}=\begin{bmatrix} -44/193 & -6/193 & 29/193 \\ 14/193 & 37/193 & -18/193 \\ 39/193 & -21/193 & 5/193 \end{bmatrix}


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