The minimum and maximum are every where.
Recall that we say m is the minimum of f on a set A if it is true that
there exist a in A such that
f(a)=m and
m<=f(x) for all x in A
If we have for example
f(x)=11 for [-10,10]
we would say f has minimum 11 on [-10,10]
depending what we were trying to do we would might further say
The minimum of f is 11 and is achived for all x such that -10<=x<=10.
I'm reviewing Meirovitch's "Methods of Analytical Dynamics," and I don't understand the commutation of the derivative from r to dr:
$$
\mathbf{F} \cdot d\mathbf{r} = m \ddot{\mathbf{r}} \cdot d\mathbf{r} = m\mathbf{\dot{r}} \cdot d\mathbf{\dot{r}}
$$