# Homework Help: Isomorphism: matrix determinant

1. Jan 19, 2009

### kala

Determine whether the given map $$\varphi$$ is an isomorphism of the first binary structure with the second.
< M2(R ), usual multiplication > with <R, usual multiplication> where $$\varphi$$(A) is the determinant of matrix A.

The determinant of the matrix is ad-bc, so $$\varphi$$(A)=ad-bc.
For this to be an isomorphism, I have to show that the function is one to one, onto and preserves the operations.
I'm having trouble getting this to work. Any suggestions?

2. Jan 19, 2009

### Hurkyl

Staff Emeritus
Maybe it can't....

3. Jan 19, 2009

### kala

According to the book it is suppose to be an isomorphism, the question says it is. I can get it to be one to one and onto, but i am having trouble with it preserving the operations.

4. Jan 19, 2009

### HallsofIvy

You just said that you must prove the function is "one to one". That is that two different matrices, such as
$$\begin{bmatrix}2 & 1 \\ 1 & 1\end{bmatrix}$$
and
$$\begin{bmatrix}3 & 2\\ 1 & 1\end{bmatrix}$$
must not have the same determinant. Is that true?

I think you should to reread that problem.

5. Jan 19, 2009

### Hurkyl

Staff Emeritus
No it doesn't. The question is asking you whether or not it is.

6. Jan 19, 2009

### kala

Oh duh... That was stupid... It doesn't have to be. Thanks