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What is the cofactor A12 of the entry 2 in the matrix with rows (1, 2) and (3, 4)?
A3
B4
C-3
D-4
Answer & Solution
Correct answer: C. -3
The minor of the entry in row 1, column 2 is 3, and the sign (-1)^(1+2) is negative, so the cofactor is -3.
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