If $a$, $b$, $c$ are the $p^{th}$, $q^{th}$, and $r^{th}$ terms of a Geometric Progression (G.P), then the angle between the vectors $\vec{u} = (\log a)\hat{i} + (\log b)\hat{j} + (\log c)\hat{k}$ and $\vec{v} = (q-r)\hat{i} + (r-p)\hat{j} + (p-q)\hat{k}$ is: