Question

Let A be an n×n matrix. Mark each statement as true or false. Justify each answer. a. An n×n determinant is define...

Let A be an n×n matrix. Mark each statement as true or false. Justify each answer.

a.

An n×n determinant is defined by determinants of (n−​1)×​(n−​1) submatrices.

b.

The​ (i,j)-cofactor of a matrix A is the matrix obtained by deleting from A its I’th row and j’th column.

a. Choose the correct answer below.

A. The statement is false. Although determinants of (n−​1)×​(n−​1)submatrices can be used to find n×n determinants,they are not involved in the definition of n×n determinants.

B. The statement is true. The determinant of an n×n

matrix A can be computed by a cofactor expansion across any row or down any column. Each term in any such expansion includes a cofactor that involves the determinant of a submatrix of size

​(n−​1)×​(n−​1).

C.  The statement is true. The determinant of an n×n

matrix A can be computed by a cofactor expansion along either diagonal. Each term in any such expansion includes a cofactor that involves the determinant of a submatrix of size

​(n−​1)×​(n−​1).

D.  The statement is false. An n×n determinant is defined by determinants of

​(n−​1)×​(n−​1)submatrices only when n>3. Determinants of 1×​1, 2×​2,and 3×3 matrices are defined separately.


b. Choose the correct answer below.

A.  The statement is false. The​ (i,j)-cofactor of a matrix A is the matrix Aij

obtained by deleting from A its jth row and ith column.

B.  The statement is false. The​ (i,j)-cofactor of A is the number

Cij=det(Aij)​,where Aij

is the submatrix obtained by deleting from A its ith row and jth column.

C.  The statement is true. It is the definition of the​ (i,j)-cofactor of a matrix A.

D.  The statement is false. The​ (i,j)-cofactor of A is the number Cij=(−1)i+jdetAij​, where Aij

is the submatrix obtained by deleting from A its ith row and jth column.

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Answer #1

a. FALSE: The statement is false. Although determinants of (n−​1)×​(n−​1)submatrices can be used to find n × n determinants, they are not involved in the definition of n × n determinants. Option A is the correct answer

b. FALSE: The statement is false. The​ (i,j)-cofactor of A is the number Cij=(−1)i+j det Aij​, where Aij

is the submatrix obtained by deleting from A its ith row and jth column. Option D is the correct answer.

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