vector-valued functions
differentiating a vector-valued function by derivating of each of the components
(vector-valued function derivatives) sum and difference property
(vector-valued function derivatives) scalar product property
(vector-valued function derivatives) dot product property
(vector-valued function derivatives) cross product property
(vector-valued function derivatives) chain product property
r(t) ⋅ r(t) = constant ⇒ r(t) ⋅ r'(t) = 0