Table of contents
- 0. Review of Algebra4h 16m
- 1. Equations & Inequalities3h 18m
- 2. Graphs of Equations43m
- 3. Functions2h 17m
- 4. Polynomial Functions1h 44m
- 5. Rational Functions1h 23m
- 6. Exponential & Logarithmic Functions2h 28m
- 7. Systems of Equations & Matrices4h 6m
- 8. Conic Sections2h 23m
- 9. Sequences, Series, & Induction1h 19m
- 10. Combinatorics & Probability1h 45m
7. Systems of Equations & Matrices
Determinants and Cramer's Rule
Problem 9d
Textbook Question
Are the given matrices inverses of each other? (Hint: Check to see whether their products are the identity matrix I↓n.) [2x2 matrix] and [2x2 matrix]

1
Step 1: Understand the concept of inverse matrices. Two matrices A and B are inverses of each other if their product is the identity matrix. For 2x2 matrices, the identity matrix is I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}.
Step 2: Multiply the given matrices. Let's denote the first matrix as A and the second matrix as B. Calculate the product AB by performing matrix multiplication.
Step 3: Perform the matrix multiplication. For matrices A = \begin{bmatrix} a & b \\ c & d \end{bmatrix} and B = \begin{bmatrix} e & f \\ g & h \end{bmatrix}, the product AB is \begin{bmatrix} ae + bg & af + bh \\ ce + dg & cf + dh \end{bmatrix}.
Step 4: Check if the resulting matrix from the multiplication is the identity matrix I = \begin{bmatrix} 1 & 0 \\ 0 & 1 \end{bmatrix}.
Step 5: If the product AB equals the identity matrix, then the matrices are inverses of each other. If not, they are not inverses.

This video solution was recommended by our tutors as helpful for the problem above
Video duration:
3mPlay a video:
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Matrix Multiplication
Matrix multiplication involves combining two matrices to produce a third matrix. For two matrices A and B to be multiplied, the number of columns in A must equal the number of rows in B. The resulting matrix's elements are calculated by taking the dot product of the rows of A with the columns of B. Understanding this operation is crucial for determining if two matrices are inverses.
Recommended video:
Finding Zeros & Their Multiplicity
Identity Matrix
An identity matrix is a square matrix with ones on the diagonal and zeros elsewhere. For a 2x2 matrix, the identity matrix is represented as I = [[1, 0], [0, 1]]. When a matrix A is multiplied by its inverse A⁻¹, the result is the identity matrix. This property is essential for verifying if two matrices are inverses of each other.
Recommended video:
Guided course
Introduction to Matrices
Inverse of a Matrix
The inverse of a matrix A, denoted A⁻¹, is a matrix that, when multiplied by A, yields the identity matrix. Not all matrices have inverses; a matrix must be square and have a non-zero determinant to possess an inverse. Checking if the product of two matrices equals the identity matrix is the primary method for confirming their inverse relationship.
Recommended video:
Graphing Logarithmic Functions
Watch next
Master Determinants of 2×2 Matrices with a bite sized video explanation from Patrick Ford
Start learningRelated Videos
Related Practice