Find the determinant of the 3×3 matrix with rows (4, 2, -1); (5, 0, 5); (5, 2, -2).

Answer and explanation

Correct answer: A.

  1. Step 1: Expand along the first row: a(ei − fh) − b(di − fg) + c(dh − eg). Step 2. Evaluating gives 20. **Answer: . Why not the others:** is what you get if you get the overall sign wrong. is what you get if you use only the first cofactor term. is what you get if you use the wrong sign on the second term.

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