Exercise · ZW-COFACTOR-LAPLACE-EXPANSION-005 · ★☆☆ Basic
Compute the cofactor \(C_{21}\) of \(\begin{pmatrix}2 & 3 \\ 5 & 7\end{pmatrix}\).
Choose one option.
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- B. \(-3\)
Explanation
Removing row 2 and column 1 leaves \(3\); the sign \((-1)^{2+1}=-1\) gives \(C_{21}=-3\).
Review the concept: Cofactor and Laplace expansion
The minor \(M\) of an entry is the determinant of the submatrix left after deleting its row and column; the cofactor \(C\) is that minor with an alternating sign.
\[C_{ij}=(-1)^{i+j}M_{ij}\]
More practice problems: cofactor and laplace expansion
- ZW-COFACTOR-LAPLACE-EXPANSION-001 For A=[1 2 3; 4 5 6; 7 8 10], compute the cofactor C_12.
- ZW-COFACTOR-LAPLACE-EXPANSION-002 For the same matrix A=[1 2 3; 4 5 6; 7 8 10], compute the minor M_23 (no sign).
- ZW-COFACTOR-LAPLACE-EXPANSION-003 Which sign (-1)^i+j corresponds to position (3,2)?
- ZW-COFACTOR-LAPLACE-EXPANSION-004 Compute det B by expanding along the first row, with B=[2 0 1; 3 1 0; 1 2 4].
- ZW-COFACTOR-LAPLACE-EXPANSION-006 Compute det[1 0 2; 3 0 1; 4 5 6] by expanding along the most convenient column.
- ZW-COFACTOR-LAPLACE-EXPANSION-007 Compute the determinant of [2 0 0 0; 1 3 0 0; 4 5 6 0; 7 8 9 1].
- ZW-COFACTOR-LAPLACE-EXPANSION-008 For A=[1 2 3; 4 5 6; 7 8 10], what is a_11C_21+a_12C_22+a_13C_23 (row 1 with the cofactors of row 2…
- ZW-COFACTOR-LAPLACE-EXPANSION-009 To compute the determinant of a 4×4 matrix by expanding along a row with no zeros, how many 3×3 det…
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