Math Problem Statement

Répond à la

On considère la matrice A = [[2, 5], [3, 8]] et sa matrice inverse A^-1 = [[8, -5], [-3, 2]]. Quelle est la matrice X telle que X * A = [[0, 1], [0, 0], [1, 0]] ?

Solution

Let's solve the problem step by step.

We are given:

  1. A matrix A=(2538)A = \begin{pmatrix} 2 & 5 \\ 3 & 8 \end{pmatrix}
  2. The inverse of matrix AA is A1=(8532)A^{-1} = \begin{pmatrix} 8 & -5 \\ -3 & 2 \end{pmatrix}.
  3. We need to find matrix XX such that XA=(010010)X \cdot A = \begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix}.

Step 1: Multiplying both sides by A1A^{-1}

To isolate XX, we can multiply both sides of the equation XA=(010010)X \cdot A = \begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix} by A1A^{-1} from the right:

XAA1=(010010)A1X \cdot A \cdot A^{-1} = \begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix} \cdot A^{-1}

Since AA1=IA \cdot A^{-1} = I (the identity matrix), this simplifies to:

X=(010010)A1X = \begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix} \cdot A^{-1}

Step 2: Performing the matrix multiplication

We need to multiply (010010)\begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix} by (8532)\begin{pmatrix} 8 & -5 \\ -3 & 2 \end{pmatrix}.

Performing the multiplication:

X=(010010)(8532)=((08+13)(05+12)(08+03)(05+02)(18+03)(15+02))X = \begin{pmatrix} 0 & 1 \\ 0 & 0 \\ 1 & 0 \end{pmatrix} \cdot \begin{pmatrix} 8 & -5 \\ -3 & 2 \end{pmatrix} = \begin{pmatrix} (0 \cdot 8 + 1 \cdot -3) & (0 \cdot -5 + 1 \cdot 2) \\ (0 \cdot 8 + 0 \cdot -3) & (0 \cdot -5 + 0 \cdot 2) \\ (1 \cdot 8 + 0 \cdot -3) & (1 \cdot -5 + 0 \cdot 2) \end{pmatrix}

This simplifies to:

X=(320085)X = \begin{pmatrix} -3 & 2 \\ 0 & 0 \\ 8 & -5 \end{pmatrix}

Step 3: Comparing with the given options

The correct matrix XX is (320085)\begin{pmatrix} -3 & 2 \\ 0 & 0 \\ 8 & -5 \end{pmatrix}, which matches option D.

Final Answer: Option D

Would you like more details or have any questions?

Here are 5 related questions you might find useful:

  1. How do you compute the inverse of a 2x2 matrix?
  2. What properties does a matrix and its inverse have when multiplied?
  3. What is the significance of multiplying by an inverse matrix in linear equations?
  4. How can you verify if a matrix multiplication result is correct?
  5. What types of matrices are not invertible?

Tip: When performing matrix multiplication, carefully follow the row-by-column method to avoid errors in the calculation!

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Math Problem Analysis

Mathematical Concepts

Matrix Multiplication
Inverse Matrices
Linear Algebra

Formulas

Matrix multiplication formula
Inverse of a 2x2 matrix: A^-1 = (1/det(A)) * [[d, -b], [-c, a]] for a 2x2 matrix A = [[a, b], [c, d]]

Theorems

Inverse Matrix Theorem
Properties of Matrix Multiplication

Suitable Grade Level

Undergraduate or High School (Advanced Level)