1. The problem statement, all variables and given/known data The question is: Let [itex]C[/itex] be a symmetric matrix of rank one. Prove that [itex]C[/itex] must have the form [itex]C=aww^T[/itex], where [itex]a[/itex] is a scalar and [itex]w[/itex] 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 [itex]C[/itex] has the form [itex]C=aww^T[/itex], then [itex]C[/itex] is symmetric and of rank one. But what about the opposite direction...that is what we need to prove. How to prove this?