Which expression represents the determinant of cap A is equal to the 2 by 2 matrix row 1, 2 3 row 2, 1 9 ?

For a 2 × 2 matrix a b; c d, the determinant is ad − bc. Here, the entries are 2, 3, 1, and 9, so det A = (2 × 9) − (3 × 1) = 2 × 9 − 1 × 3. This matches choice A.

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