## recessive space proof

Hello,

I need to prove that $=0 \Longleftrightarrow F''(x)h=0$ where $F''(x)$ is the hessian matrix and therefore is PSD $\Longrightarrow F''(x)=R^TR$ (Cholesky).

Trying to prove the first direction I basically end with $h^TR^TRh=0$ but can not see why it implies that $R^TRh=0$