1. Let r(t) = (x(t), y(t), z(t)) be a vector valued function of 1 variable, where x(t), y(t), z(t) are continuously differentiable. Show that if |r(t) is a constant function, for simplicity lets say |r(t) | = 100 for every t, then r(t) . r/(t) = 0 for every t. Pictorially, this means r(t) I ri (t) for every t