# Form of symmetric matrix of rank one

1. Apr 16, 2013

### ianchenmu

1. The problem statement, all variables and given/known data

The question is:

Let $C$ be a symmetric matrix of rank one. Prove that $C$ must have the form $C=aww^T$, where $a$ is a scalar and $w$ is a vector of norm one.

2. Relevant equations
n/a

3. The attempt at a solution
I think we can easily prove that if $C$ has the form $C=aww^T$, then $C$ is symmetric and of rank one. But what about the opposite direction...that is what we need to prove. How to prove this?

2. Apr 16, 2013

### Dick

Do you know that if C is symmetric, it can be diagonalized?