Matrices: Transpose and Inverse

For the given problem, you need to be careful with the order of operations. You should do the inverse of Y and X before transposing, because transposing changes the order of the matrices. In summary, to solve the given problem, you need to first find the inverse of Y and X, then multiply Y-1 by X and transpose, and finally subtract the transposed matrices to get the correct answer of [-3 -2] and [6 3]. It is important to remember the order of operations when dealing with matrices, as they are not always commutative.
  • #1
PotentialE
57
0

Homework Statement


Find (X * Y-1)T - (Y * X-1)T
When X = [3 5]
.....[1 2]
and Y = [3 4]
...[2 3]

Homework Equations


Inverse= 1/ad-bc [d -b]
......[-c a]

The Attempt at a Solution


I got:
[9 -6 ]
[14 -9]

But the answer is:
[-3 -2]
[6 3]I did the problem twice and got the same answer so I don't think its a simple math error, any insight as to how to solve this correctly / what I've done wrong?
 
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  • #2
It's rather hard to say where you've gone wrong without seeing your working. Your equations are correct.
 
  • #3
Well first I did the inverse of Y and got:
[3 -4]
[-2 3]

Then I multiplied that by X and got:
[5 7]
[-3 -4]

Then I transposed it and got:
[5 -3]
[7 -4]

Then I did the inverse of X and got:
[2 -5]
[-1 3]

Multiplied by Y and got:
[-4 -7]
[3 5]

Then I transposed that and got:
[-4 3]
[-7 5]

Then I subtracted the two transposed matrices to get:
[9 -6]
[14 -9]

Seems coherent to me but it's very far from the right answer
 
  • #4
In your second step, looks like you did Y-1*X instead of X*Y-1
 
  • #5
Oh that's right! I forgot the associative property is non-applicable to matrices. THanks for your help.
 
  • #6
PotentialE said:
I forgot the associative property is non-applicable to matrices.
No, matrices are associative, A(BC) = (A B)C, but they are not always commutative.
 

1. What is the transpose of a matrix?

The transpose of a matrix is a new matrix in which the rows of the original matrix are now the columns, and the columns are now the rows. This means that the elements of the first row of the original matrix will become the first column of the transposed matrix, and so on.

2. How do I calculate the transpose of a matrix?

To calculate the transpose of a matrix, simply switch the rows and columns of the original matrix. For a matrix with dimensions m x n, the transposed matrix will have dimensions n x m. You can also use the transpose function in most programming languages to calculate the transpose of a matrix.

3. What is an inverse matrix?

An inverse matrix is a matrix that, when multiplied by the original matrix, results in the identity matrix. The identity matrix is a square matrix with 1s along the main diagonal and 0s everywhere else. In other words, an inverse matrix "undoes" the effects of the original matrix.

4. How do I find the inverse of a matrix?

To find the inverse of a matrix, you can use the Gauss-Jordan elimination method or use a matrix calculator. The Gauss-Jordan elimination method involves performing row operations on the original matrix until it is reduced to the identity matrix, with the same operations performed on an identity matrix to get the inverse. Matrix calculators use algorithms to find the inverse directly.

5. Can every matrix be inverted?

No, not every matrix can be inverted. A matrix can only be inverted if it is a square matrix (same number of rows and columns) and has a non-zero determinant. If a matrix cannot be inverted, it is known as a singular or non-invertible matrix.

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