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Expanding by Minors along the First Row to Evaluate a 3 × 3 Determinant

To evaluate a 3imes33 imes 3 determinant by expanding by minors along the first row, each entry in the first row is multiplied by its corresponding minor (the 2imes22 imes 2 determinant remaining after the entry's row and column are removed), and the results are combined using the alternating sign pattern +,,++, -, +. Specifically, for a 3imes33 imes 3 determinant with first-row entries a1a_1, b1b_1, and c1c_1, the value equals a1a_1 times the minor of a1a_1, minus b1b_1 times the minor of b1b_1, plus c1c_1 times the minor of c1c_1.

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Updated 2026-05-25

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Intermediate Algebra @ OpenStax

Algebra

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