Math Problem Statement

Let A, B, and C be 3×3 matrices, with det(A) = 2, det(B) = 6, and det(C) = 3. What is det(2B⁻¹C²AᵀB)?

Solution

To solve the problem det(2B1C2ATB)\det(2B^{-1}C^2A^TB), let’s break it down step by step.

Given:

  • det(A)=2\det(A) = 2,
  • det(B)=6\det(B) = 6,
  • det(C)=3\det(C) = 3.

Key Properties of Determinants:

  1. Scalar Multiplication: If kk is a scalar and AA is a matrix, then det(kA)=kndet(A)\det(kA) = k^n \det(A), where nn is the dimension of AA. Since the matrices are 3×33 \times 3, n=3n = 3.
  2. Inverse Matrix: For an invertible matrix BB, det(B1)=1det(B)\det(B^{-1}) = \frac{1}{\det(B)}.
  3. Product of Matrices: For matrices XX and YY, det(XY)=det(X)det(Y)\det(XY) = \det(X)\det(Y).
  4. Transpose: For any matrix AA, det(AT)=det(A)\det(A^T) = \det(A).

Steps:

  1. Start with the expression: det(2B1C2ATB).\det(2B^{-1}C^2A^TB).

  2. Break it into parts: Using the determinant property for matrix products: det(2B1C2ATB)=det(2)det(B1)det(C2)det(AT)det(B).\det(2B^{-1}C^2A^TB) = \det(2) \cdot \det(B^{-1}) \cdot \det(C^2) \cdot \det(A^T) \cdot \det(B).

  3. Compute each determinant:

    • det(2)=23=8\det(2) = 2^3 = 8 (since it’s a scalar multiplied to a 3×33 \times 3 matrix).
    • det(B1)=1det(B)=16\det(B^{-1}) = \frac{1}{\det(B)} = \frac{1}{6}.
    • det(C2)=(det(C))2=32=9\det(C^2) = (\det(C))^2 = 3^2 = 9.
    • det(AT)=det(A)=2\det(A^T) = \det(A) = 2 (property of the determinant under transpose).
    • det(B)=6\det(B) = 6 (given).
  4. Substitute these values: det(2B1C2ATB)=816926.\det(2B^{-1}C^2A^TB) = 8 \cdot \frac{1}{6} \cdot 9 \cdot 2 \cdot 6.

  5. Simplify:

    • First, compute 816=86=438 \cdot \frac{1}{6} = \frac{8}{6} = \frac{4}{3},
    • Then, 439=12\frac{4}{3} \cdot 9 = 12,
    • Then, 122=2412 \cdot 2 = 24,
    • Finally, 246=14424 \cdot 6 = 144.

Final Answer:

The determinant det(2B1C2ATB)=144\det(2B^{-1}C^2A^TB) = 144.

Correct Option:

b) 144

Would you like a further explanation, or do you have any questions?


Here are some related questions you might find helpful:

  1. How is the determinant of a product of matrices computed?
  2. Why does det(AT)=det(A)\det(A^T) = \det(A) hold true?
  3. What is the effect of a scalar on a determinant?
  4. How does the determinant of an inverse matrix work?
  5. Can the determinant be negative, and what does it imply?

Tip: When working with determinants, always break down the expression using determinant properties systematically for clarity.

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Math Problem Analysis

Mathematical Concepts

Matrix Algebra
Determinants

Formulas

det(kA) = k^n det(A), where n is the dimension of the matrix
det(Aᵀ) = det(A)
det(B⁻¹) = 1 / det(B)
det(AB) = det(A) * det(B)

Theorems

Determinant Properties for Matrices

Suitable Grade Level

Undergraduate (First Year or Advanced High School)