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Let A=[aij]A = [a_{ij}] is given by A=[1−1234−52−13]A = \begin{bmatrix} 1 & -1 & 2 \\ 3 & 4 & -5 \\ 2 & -1 & 3 \end{bmatrix}. Then the matrix B=[bij]B = [b_{ij}], where bijb_{ij} = Minor of aija_{ij} is:

Solution

✅ Correct Option: 1

Given: A=[1−1234−52−13]A = \begin{bmatrix} 1 & -1 & 2 \\ 3 & 4 & -5 \\ 2 & -1 & 3 \end{bmatrix}

The minor of an element aija_{ij} is the determinant of the matrix obtained by deleting row ii and column jj.


For b11b_{11}, delete row 1 and column 1:

[4−5−13]\begin{bmatrix} 4 & -5 \\ -1 & 3 \end{bmatrix}

b11=(4)(3)−(−5)(−1)b_{11} = (4)(3) - (-5)(-1)

b11=12−5b_{11} = 12 - 5

b11=7b_{11} = 7


For b12b_{12}, delete row 1 and column 2:

[3−523]\begin{bmatrix} 3 & -5 \\ 2 & 3 \end{bmatrix}

b12=(3)(3)−(−5)(2)b_{12} = (3)(3) - (-5)(2)

b12=9+10b_{12} = 9 + 10

b12=19b_{12} = 19


For b13b_{13}, delete row 1 and column 3:

[342−1]\begin{bmatrix} 3 & 4 \\ 2 & -1 \end{bmatrix}

b13=(3)(−1)−(4)(2)b_{13} = (3)(-1) - (4)(2)

b13=−3−8b_{13} = -3 - 8

b13=−11b_{13} = -11


For b21b_{21}, delete row 2 and column 1:

[−12−13]\begin{bmatrix} -1 & 2 \\ -1 & 3 \end{bmatrix}

b21=(−1)(3)−(2)(−1)b_{21} = (-1)(3) - (2)(-1)

b21=−3+2b_{21} = -3 + 2

b21=−1b_{21} = -1


For b22b_{22}, delete row 2 and column 2:

[1223]\begin{bmatrix} 1 & 2 \\ 2 & 3 \end{bmatrix}

b22=(1)(3)−(2)(2)b_{22} = (1)(3) - (2)(2)

b22=3−4b_{22} = 3 - 4

b22=−1b_{22} = -1


For b23b_{23}, delete row 2 and column 3:

[1−12−1]\begin{bmatrix} 1 & -1 \\ 2 & -1 \end{bmatrix}

b23=(1)(−1)−(−1)(2)b_{23} = (1)(-1) - (-1)(2)

b23=−1+2b_{23} = -1 + 2

b23=1b_{23} = 1


For b31b_{31}, delete row 3 and column 1:

[−124−5]\begin{bmatrix} -1 & 2 \\ 4 & -5 \end{bmatrix}

b31=(−1)(−5)−(2)(4)b_{31} = (-1)(-5) - (2)(4)

b31=5−8b_{31} = 5 - 8

b31=−3b_{31} = -3


For b32b_{32}, delete row 3 and column 2:

[123−5]\begin{bmatrix} 1 & 2 \\ 3 & -5 \end{bmatrix}

b32=(1)(−5)−(2)(3)b_{32} = (1)(-5) - (2)(3)

b32=−5−6b_{32} = -5 - 6

b32=−11b_{32} = -11


For b33b_{33}, delete row 3 and column 3:

[1−134]\begin{bmatrix} 1 & -1 \\ 3 & 4 \end{bmatrix}

b33=(1)(4)−(−1)(3)b_{33} = (1)(4) - (-1)(3)

b33=4+3b_{33} = 4 + 3

b33=7b_{33} = 7


Therefore, the matrix of minors is:

B=[719−11−1−11−3−117]B = \begin{bmatrix} 7 & 19 & -11 \\ -1 & -1 & 1 \\ -3 & -11 & 7 \end{bmatrix}

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