Mathematics
Grade 12
15 min
Inverse of a 2 x 2 matrix
Inverse of a 2 x 2 matrix
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1
Introduction & Learning Objectives
Learning Objectives
Define the identity matrix and its role in matrix operations.
Accurately calculate the determinant of any 2x2 matrix.
Determine if a 2x2 matrix is singular or non-singular and explain what this implies about its inverse.
State and apply the formula to find the inverse of a non-singular 2x2 matrix.
Verify the inverse of a matrix by showing that A * A⁻¹ = I.
Solve a system of two linear equations using the inverse matrix method.
How can you 'undo' a transformation or unscramble a secret message? 🤔 Finding the inverse of a matrix is the key!
This tutorial will guide you through the process of finding the inverse of a 2x2 matrix. You'll learn what an inverse is, how to calculate it using a specific formula, and why it's a powerful tool,...
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Key Concepts & Vocabulary
TermDefinitionExample
Identity Matrix (I)The square matrix that acts as the multiplicative identity. When any matrix is multiplied by the identity matrix, it remains unchanged. For 2x2 matrices, it is a matrix with 1s on the main diagonal and 0s elsewhere.The 2x2 identity matrix is I = [[1, 0], [0, 1]]. For any 2x2 matrix A, A * I = I * A = A.
Determinant (det(A) or |A|)A unique scalar value calculated from the elements of a square matrix. The determinant provides important information about the matrix, most notably whether an inverse exists.For A = [[a, b], [c, d]], the determinant is det(A) = ad - bc. For A = [[4, 1], [3, 2]], det(A) = (4)(2) - (1)(3) = 8 - 3 = 5.
Inverse Matrix (A⁻¹)The matrix that, when multiplied by the original matrix A, yields the identity matrix I. It is analogous...
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Core Formulas
Determinant of a 2x2 Matrix
If A = \begin{pmatrix} a & b \\ c & d \end{pmatrix}, then det(A) = ad - bc
This formula is the first step in finding the inverse. Multiply the elements on the main diagonal (top-left to bottom-right) and subtract the product of the elements on the other diagonal (top-right to bottom-left).
Formula for the Inverse of a 2x2 Matrix
If A = \begin{pmatrix} a & b \\ c & d \end{pmatrix}, then A^{-1} = \frac{1}{ad-bc} \begin{pmatrix} d & -b \\ -c & a \end{pmatrix}
This formula is used only if the determinant (ad-bc) is not zero. To apply it, you take the reciprocal of the determinant and multiply it by a new matrix formed by swapping elements 'a' and 'd' and negating elements 'b' and 'c'....
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Challenging
For what value(s) of k is the matrix A = \begin{pmatrix} k-1 & 2 \\ 4 & k+1 \end{pmatrix} singular?
A.k = 0
B.k = 1 and k = -1
C.k = 3 and k = -3
D.k = 9
Challenging
The inverse of a matrix A is given by A⁻¹ = \begin{pmatrix} 4 & -3 \\ -1 & 1 \end{pmatrix}. What is the original matrix A?
A.\begin{pmatrix} 1 & 1 \\ 3 & 4 \end{pmatrix}
B.\begin{pmatrix} 1 & 3 \\ 1 & 4 \end{pmatrix}
C.\begin{pmatrix} 1/4 & -1/3 \\ -1 & 1 \end{pmatrix}
D.\begin{pmatrix} 4 & 1 \\ 3 & 1 \end{pmatrix}
Challenging
Given the matrix equation \begin{pmatrix} 3 & -2 \\ -4 & 3 \end{pmatrix} \begin{pmatrix} x \\ y \end{pmatrix} = \begin{pmatrix} 8 \\ 5 \end{pmatrix}, solve for x and y.
A.x = 14, y = 17
B.x = 2, y = -1
C.x = 1, y = -2.5
D.x = 34, y = 47
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