# Constructing isomorphisms

1. Nov 22, 2011

### retracell

1. The problem statement, all variables and given/known data
Construct an isomorphism from a 2 by 2 symmetric matrix to R^3.

2. Relevant equations
N/A

3. The attempt at a solution
I know that for a transformation to be an isomorphic, it must be one-to-one and onto. Would the transform be T:A->R^3 and I would have to choose a general matrix A to test?

How would I test it not knowing how the transform is mapped?

2. Nov 22, 2011

### micromass

Staff Emeritus
An isomorphism between which structure?? Vector spaces??

Anyway, given a symmetric matrix

$$\left(\begin{array}{cc} a & b\\ b & c \end{array}\right)$$

what element of $\mathbb{R}^3$ would you associate with this matrix??

3. Nov 22, 2011

### retracell

Yes vector spaces. What do you mean by what element? Would R^3 simply be some vector v=(v1, v2, v3)?

4. Nov 22, 2011

### micromass

Staff Emeritus

Yes, elements of $\mathbb{R}^3$ would just be vectors (a,b,c).

5. Nov 22, 2011

### retracell

So then I would just check the the nullspace and the dimension of the range? What would be the form of my answer? A matrix?

6. Nov 22, 2011

### micromass

Staff Emeritus
You still need a suggestion for what your isomorphism actually does. To which matrix would you map (a,b,c)?? That is: if I give you three real numbers, how would you make a symmetric matrix out of it??