Let $k$, $l$ be smooth functions from an interval $I$ into $\mathbb R$ and $k>0$. Let's consider system of differential equations
$$ t'=k n, $$ $$ n'=-k t-l b, $$ $$ b'=ln $$ with unknow functions $t,n,b: I\rightarrow \mathbb R^3$.
How to show that scalar products below are zero: $$ t\cdot t'=0, $$ $$ n\cdot n'=0, $$ $$ b\cdot b'=0. $$
Thanks