Math Problem Statement

Diketahui matriks A = [ [1, 2], [3, 5] ] dan B = [ [3, -2], [1, 4] ]. Jika A^T adalah transpose dari matriks A dan AX - B + A^T = 0, maka determinan matriks X adalah?

Solution

The problem provided is about matrices. From the image, the matrices AA and BB are defined as:

A=(1235),B=(3214)A = \begin{pmatrix} 1 & 2 \\ 3 & 5 \end{pmatrix}, \quad B = \begin{pmatrix} 3 & -2 \\ 1 & 4 \end{pmatrix}

The task involves matrix ATA^T, which is the transpose of matrix AA, and an equation involving AXB+AT=0AX - B + A^T = 0, where the goal is to find the determinant of matrix XX.

Steps to solve:

  1. Transpose of Matrix AA: The transpose ATA^T is found by swapping rows and columns of AA: AT=(1325)A^T = \begin{pmatrix} 1 & 3 \\ 2 & 5 \end{pmatrix}

  2. Equation Setup: The equation is AXB+AT=0AX - B + A^T = 0. Rearranging this to isolate XX, we get: AX=BATAX = B - A^T Hence, we first need to compute BATB - A^T.

  3. Matrix Subtraction BATB - A^T: Perform element-wise subtraction:

    = \begin{pmatrix} 3 - 1 & -2 - 3 \\ 1 - 2 & 4 - 5 \end{pmatrix} = \begin{pmatrix} 2 & -5 \\ -1 & -1 \end{pmatrix}$$
  4. Solve for XX: Now, AX=(2511)AX = \begin{pmatrix} 2 & -5 \\ -1 & -1 \end{pmatrix}. To find XX, we need to multiply both sides of the equation by the inverse of AA, i.e., X=A1((2511))X = A^{-1} \left( \begin{pmatrix} 2 & -5 \\ -1 & -1 \end{pmatrix} \right)

    First, calculate the inverse of AA.

  5. Inverse of Matrix AA: The inverse of a 2x2 matrix A=(abcd)A = \begin{pmatrix} a & b \\ c & d \end{pmatrix} is given by: A1=1adbc(dbca)A^{-1} = \frac{1}{ad - bc} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix} For A=(1235)A = \begin{pmatrix} 1 & 2 \\ 3 & 5 \end{pmatrix}: Det(A)=(1)(5)(2)(3)=56=1\text{Det}(A) = (1)(5) - (2)(3) = 5 - 6 = -1 Therefore, the inverse of AA is: A1=11(5231)=(5231)A^{-1} = \frac{1}{-1} \begin{pmatrix} 5 & -2 \\ -3 & 1 \end{pmatrix} = \begin{pmatrix} -5 & 2 \\ 3 & -1 \end{pmatrix}

  6. Multiplying to find XX: Now, multiply A1A^{-1} with BATB - A^T: X=(5231)(2511)X = \begin{pmatrix} -5 & 2 \\ 3 & -1 \end{pmatrix} \begin{pmatrix} 2 & -5 \\ -1 & -1 \end{pmatrix} Perform the matrix multiplication: X=((5)(2)+(2)(1)(5)(5)+(2)(1)(3)(2)+(1)(1)(3)(5)+(1)(1))X = \begin{pmatrix} (-5)(2) + (2)(-1) & (-5)(-5) + (2)(-1) \\ (3)(2) + (-1)(-1) & (3)(-5) + (-1)(-1) \end{pmatrix} X=(1022526+115+1)=(1223714)X = \begin{pmatrix} -10 - 2 & 25 - 2 \\ 6 + 1 & -15 + 1 \end{pmatrix} = \begin{pmatrix} -12 & 23 \\ 7 & -14 \end{pmatrix}

  7. Determinant of XX: Finally, the determinant of XX is: Det(X)=(12)(14)(23)(7)=168161=7\text{Det}(X) = (-12)(-14) - (23)(7) = 168 - 161 = 7

Thus, the determinant of matrix XX is 7.

Would you like more details on any step or further explanation?


Here are 5 related questions to expand your understanding:

  1. How do you calculate the determinant of a 3x3 matrix?
  2. What properties of determinants are useful when multiplying matrices?
  3. Can the determinant of a matrix be zero? If so, what does that imply about the matrix?
  4. How do you solve matrix equations involving inverses if the matrix is singular?
  5. What is the geometric interpretation of the determinant of a matrix?

Tip: The determinant of a matrix not only helps in solving equations but also provides insight into whether the matrix is invertible or not (non-zero determinant means invertible).

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Math Problem Analysis

Mathematical Concepts

Matrices
Matrix Transpose
Matrix Inversion
Determinants

Formulas

Transpose of a matrix: A^T
Matrix equation: AX - B + A^T = 0
Inverse of a 2x2 matrix: A^{-1} = (1/det(A)) * [[d, -b], [-c, a]]
Determinant of a 2x2 matrix: det(A) = ad - bc

Theorems

Matrix inversion
Properties of determinants

Suitable Grade Level

Grades 10-12