How can you find the inverse of a matrix A when given A and AB?

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In summary, to determine a matrix B when given A and AB, you can use the inverse of A by multiplying it on the left side of AB to get B. This is based on the fact that multiplying a matrix by its inverse results in the identity matrix, which when multiplied by any matrix gives the original matrix back. However, if A does not have an inverse, there may be multiple solutions for B.
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General question:
How do you determine a matrix B when given A and AB?
 
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If you know the inverse of A, you can multiply on the left side by A^-1 to get B, i.e. (A^-1)AB = B.
 
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Oh I see. I understand the computation, but could you explain the theory behind this?
 
  • #4
This isn't exactly a thorough explanation, but basically if you multiply a matrix by its inverse, you get the identity matrix I. If you multiply any matrix by the identity matrix, you get the original matrix back again, e.g. IA = AI = A.
 
  • #5
The theory? A guess it's things like "associative law" and "existence of the multiplicative identity"!
If you were given two numbers a, c, a not equal to 0, and told that ab= c, how would you solve for b?

If A has an inverse, then A-1(AB)= (A-1A)B= IB= B.

Notice the condition "If A has an inverse". There are plenty of different matrices, A, B, not having inverses, such that AB= 0. If A does not have an inverse, there may be many different matrices B such that AB= C.
 

FAQ: How can you find the inverse of a matrix A when given A and AB?

What is a matrix?

A matrix is a rectangular array of numbers, symbols, or expressions arranged in rows and columns. It is commonly used in mathematics and science to represent and manipulate data and equations.

Why is it important to determine an unknown matrix?

Determining an unknown matrix is important in various fields such as statistics, economics, and engineering. It allows us to analyze and understand data, solve equations, and make predictions.

What are the methods for determining an unknown matrix?

There are several methods for determining an unknown matrix, including Gaussian elimination, Cramer's rule, and the inverse matrix method. These methods involve performing operations on the matrix to solve for its unknown values.

How do you know if a matrix has a unique solution?

A matrix has a unique solution if it is a square matrix and its determinant is non-zero. This means that there is one and only one set of values that satisfy the equations represented by the matrix.

Can an unknown matrix have more than one solution?

Yes, an unknown matrix can have more than one solution. This can happen when the matrix is not a square matrix or when its determinant is equal to zero, indicating that there are multiple sets of values that satisfy the equations represented by the matrix.

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