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Which of the following are correct?

(A) For a square matrix A, if A³ = I, then A⁻¹ = A².

(B) The determinant of only a square matrix can be defined.

(C) If A is a square matrix of order 3, then the number of minors of the matrix A is 3.

(D) If A and B are two non-singular matrices of the same order, then (AB)⁻¹ = B⁻¹A⁻¹.

Choose the correct answer from the options given below:

Solution

Correct Option: 1

For statement (A), given that A3=IA^3 = I where II is the identity matrix.

A3=IA^3 = I

AA2=IA \cdot A^2 = I

By the definition of inverse matrix, if AA2=IA \cdot A^2 = I, then A2A^2 is the inverse of AA.

Therefore, A1=A2A^{-1} = A^2

Statement (A) is correct.


For statement (B), determinants are only defined for square matrices where the number of rows equals the number of columns.

A determinant can be found for a 2×22 \times 2 or 3×33 \times 3 matrix, but cannot be found for a 2×32 \times 3 or 3×23 \times 2 matrix.

Statement (B) is correct.


For statement (C), a minor is the determinant obtained after removing one row and one column.

For a 3×33 \times 3 matrix:

Number of choices for removing a row =3= 3

Number of choices for removing a column =3= 3

Total number of minors =3×3=9= 3 \times 3 = 9

Statement (C) is incorrect. The number of minors is 9, not 3.


For statement (D), this is a standard property of matrix inverses.

To verify that (AB)1=B1A1(AB)^{-1} = B^{-1}A^{-1}:

(AB)(B1A1)(AB) \cdot (B^{-1}A^{-1})

=A(BB1)A1= A(B \cdot B^{-1})A^{-1}

=AIA1= A \cdot I \cdot A^{-1}

=AA1= A \cdot A^{-1}

=I= I

Statement (D) is correct.


Statements (A), (B), and (D) are correct.

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