Math Problem Statement

Find where possible the inverses of the following matrices: A = (3 1 | 3 2), B = (1 4 | -3 2), C = (3 4 | -3 -6). If an inverse cannot be obtained, state the reason behind this result.

Solution

To find the inverses of the given matrices AA, BB, and CC, we need to check if each matrix is invertible. A matrix is invertible if its determinant is non-zero. If the determinant is zero, the matrix is singular, and no inverse exists.

Matrix AA:

A=(3132)A = \begin{pmatrix} 3 & 1 \\ 3 & 2 \end{pmatrix} The determinant of AA is: det(A)=(3)(2)(1)(3)=63=3\text{det}(A) = (3)(2) - (1)(3) = 6 - 3 = 3 Since the determinant of AA is 3 (non-zero), the matrix is invertible. The inverse of a 2x2 matrix (abcd)\begin{pmatrix} a & b \\ c & d \end{pmatrix} is given by: A1=1det(A)(dbca)A^{-1} = \frac{1}{\text{det}(A)} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix} Applying this formula to matrix AA: A1=13(2133)=(231311)A^{-1} = \frac{1}{3} \begin{pmatrix} 2 & -1 \\ -3 & 3 \end{pmatrix} = \begin{pmatrix} \frac{2}{3} & -\frac{1}{3} \\ -1 & 1 \end{pmatrix}

Matrix BB:

B=(1432)B = \begin{pmatrix} 1 & 4 \\ -3 & 2 \end{pmatrix} The determinant of BB is: det(B)=(1)(2)(4)(3)=2+12=14\text{det}(B) = (1)(2) - (4)(-3) = 2 + 12 = 14 Since the determinant of BB is 14 (non-zero), the matrix is invertible. Using the inverse formula: B1=114(2431)=(214414314114)=(1727314114)B^{-1} = \frac{1}{14} \begin{pmatrix} 2 & -4 \\ 3 & 1 \end{pmatrix} = \begin{pmatrix} \frac{2}{14} & -\frac{4}{14} \\ \frac{3}{14} & \frac{1}{14} \end{pmatrix} = \begin{pmatrix} \frac{1}{7} & -\frac{2}{7} \\ \frac{3}{14} & \frac{1}{14} \end{pmatrix}

Matrix CC:

C=(3436)C = \begin{pmatrix} 3 & 4 \\ -3 & -6 \end{pmatrix} The determinant of CC is: det(C)=(3)(6)(4)(3)=18+12=6\text{det}(C) = (3)(-6) - (4)(-3) = -18 + 12 = -6 Since the determinant of CC is -6 (non-zero), the matrix is invertible. Using the inverse formula: C1=16(6433)=(1231212)C^{-1} = \frac{1}{-6} \begin{pmatrix} -6 & -4 \\ 3 & 3 \end{pmatrix} = \begin{pmatrix} 1 & \frac{2}{3} \\ -\frac{1}{2} & -\frac{1}{2} \end{pmatrix}

Summary:

  • A1=(231311)A^{-1} = \begin{pmatrix} \frac{2}{3} & -\frac{1}{3} \\ -1 & 1 \end{pmatrix}
  • B1=(1727314114)B^{-1} = \begin{pmatrix} \frac{1}{7} & -\frac{2}{7} \\ \frac{3}{14} & \frac{1}{14} \end{pmatrix}
  • C1=(1231212)C^{-1} = \begin{pmatrix} 1 & \frac{2}{3} \\ -\frac{1}{2} & -\frac{1}{2} \end{pmatrix}

Would you like more details on the calculation steps or have any other questions?

Here are some follow-up questions for further exploration:

  1. What is the significance of the determinant in determining the invertibility of a matrix?
  2. How does matrix inversion apply to solving systems of linear equations?
  3. Can we use a different method, like Gaussian elimination, to find the inverse of a matrix?
  4. How does the inverse of a matrix relate to its transpose and adjugate?
  5. What is the computational complexity of finding the inverse of a matrix in larger systems?

Tip: Always check the determinant before attempting to find the inverse of a matrix, as it will save time if the matrix is singular.

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Math Problem Analysis

Mathematical Concepts

Matrix Inversion
Linear Algebra

Formulas

Determinant of a 2x2 matrix det(A) = ad - bc
Inverse of a 2x2 matrix A = [[a, b], [c, d]] is A^-1 = (1/det(A)) * [[d, -b], [-c, a]]

Theorems

Matrix Inversion Theorem: A matrix is invertible if its determinant is non-zero.
Determinant Theorem: If det(A) = 0, the matrix A is singular and non-invertible.

Suitable Grade Level

Undergraduate Mathematics