Engineering Board Exam Reviewer · Matrix Inverse and Cofactors · medium

Find the (1,2) entry of A-1 if A= bmatrix1&2&1\0&1&3\2&1&0 bmatrix.

1. 67
2. - 17
3. 17
4. 1

Answer

C. 17

Solution

A=7. The (1,2) entry of A-1 is C21 A (the adjugate is the transposed cofactor matrix). C21=(-1)3 vmatrix2&1\1&0 vmatrix=-(0-1)=1, so the entry is 17.

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