Math Problem Statement

Consider the 3x3 matrices A and B, where det A = 2 and det B = 5. What is det [(3A)^-1B^2]?

A. 25/6 B. -675/2 C. 1350 D. 25/54

Solution

We are given two 3x3 matrices AA and BB, with det(A)=2\det(A) = 2 and det(B)=5\det(B) = 5. We need to find det((3A)1B2)\det \left( (3A)^{-1} B^2 \right).

Step 1: Determinant properties

We will use the following properties of determinants:

  1. det(AB)=det(A)det(B)\det(AB) = \det(A) \cdot \det(B) for any square matrices AA and BB.
  2. det(A1)=1det(A)\det(A^{-1}) = \frac{1}{\det(A)} for an invertible matrix AA.
  3. det(cA)=cndet(A)\det(cA) = c^n \det(A) for an n×nn \times n matrix AA and scalar cc, where nn is the dimension of the matrix.

Step 2: Determinant of (3A)1(3A)^{-1}

First, calculate the determinant of 3A3A: det(3A)=33det(A)=272=54\det(3A) = 3^3 \det(A) = 27 \cdot 2 = 54 Now, the determinant of (3A)1(3A)^{-1} is: det((3A)1)=1det(3A)=154\det \left( (3A)^{-1} \right) = \frac{1}{\det(3A)} = \frac{1}{54}

Step 3: Determinant of B2B^2

We know that det(B2)=(det(B))2\det(B^2) = (\det(B))^2. Therefore: det(B2)=52=25\det(B^2) = 5^2 = 25

Step 4: Determinant of the product

Now, use the property det(AB)=det(A)det(B)\det(AB) = \det(A) \cdot \det(B): det((3A)1B2)=det((3A)1)det(B2)=15425=2554\det \left( (3A)^{-1} B^2 \right) = \det \left( (3A)^{-1} \right) \cdot \det(B^2) = \frac{1}{54} \cdot 25 = \frac{25}{54}

Thus, the answer is: D.2554\boxed{D. \frac{25}{54}}

Would you like a deeper explanation of any step?

Here are some related questions to explore:

  1. How do you find the inverse of a matrix?
  2. What are the properties of matrix multiplication with determinants?
  3. How does the determinant change under scalar multiplication?
  4. How can determinants help in solving systems of linear equations?
  5. What is the geometric interpretation of the determinant of a matrix?

Tip: Understanding matrix determinant properties simplifies many problems involving matrices.

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Math Problem Analysis

Mathematical Concepts

Matrix Algebra
Determinants
Matrix Inverses

Formulas

det(AB) = det(A) * det(B)
det(A^-1) = 1 / det(A)
det(cA) = c^n * det(A), where n is the matrix size
det(B^2) = (det(B))^2

Theorems

Multiplicative Property of Determinants
Inverse Matrix Determinant Theorem
Scalar Multiplication of Matrices

Suitable Grade Level

Undergraduate Level (Linear Algebra)