A curve is defined by $\displaystyle r(t)$ such that $\displaystyle r'(t) \neq 0$

$\displaystyle T(t)=\frac{r'(t)}{|r'(t)|}$

Show that T and T' are always orthogonal by using |T|=1

edit: this should only take a few lines of working

i've tried using dot product =0 because the angle is 90 but i've no idea where to take that from there