Can You Find Matrices B and C Where AB = AC but B ≠ C?

  • Context: Undergrad 
  • Thread starter Thread starter LaraCroft
  • Start date Start date
  • Tags Tags
    Matrix Suggestions
Click For Summary
SUMMARY

The discussion centers on finding two distinct 2x2 matrices B and C such that the equation AB = AC holds true, where A is defined as A = [[-3, 9], [-1, 3]]. The key insight is that matrix A has a rank of 1, indicating that any components of B and C that lie in the null space of A will yield the same product when multiplied by A. Participants suggest using variables for the elements of matrix B and performing row reduction on A to explore the relationships between B and C without affecting the outcome.

PREREQUISITES
  • Understanding of matrix multiplication
  • Knowledge of matrix rank and null space concepts
  • Familiarity with row reduction techniques
  • Basic linear algebra principles
NEXT STEPS
  • Explore the concept of matrix rank and its implications in linear transformations
  • Learn about null spaces and how they relate to matrix equations
  • Study row reduction methods and their applications in solving matrix equations
  • Investigate the properties of linear transformations and their effects on matrices
USEFUL FOR

Students and professionals in mathematics, particularly those studying linear algebra, as well as educators looking for examples of matrix properties and operations.

LaraCroft
Messages
14
Reaction score
0
Let A =

[ -3 9 ]
[ -1 3 ]

Find two 2x2 matrices B and C, such that AB = AC BUT B does not equal C.

I am stumped, but I am trying inverses and such, with no luck :(

Any insight would be great!:wink:
 
Physics news on Phys.org
LaraCroft said:
Let A =

[ -3 9 ]
[ -1 3 ]

Find two 2x2 matrices B and C, such that AB = AC BUT B does not equal C.

I am stumped, but I am trying inverses and such, with no luck :(

Any insight would be great!:wink:

Matrix A has rank 1. Any component of the column vectors in B and C in the null space of A will be mapped to zero. This leaves quite a few possibilities.

However, if you haven't learned about null spaces yet, Just use variables for the ellements of the B matrix, multiply A by B and see how these variables can be changed without affecting the product.

This might be more clear if you row reduce A. Remember that each row operation can be represented by a linear transformation. Doing the row operation on the identity matrix will give you the desired transformation. Therefor you can safely row reduce A without affecting the solution to the problem.
 

Similar threads

Replies
3
Views
2K
Replies
13
Views
4K
  • · Replies 33 ·
2
Replies
33
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 1 ·
Replies
1
Views
1K