Do you know the McLaurin series for ln(1+ x)? If not, it's easy to differentiate that repeatedly and just using the definition of McLaurin series. Once you have that, replace x with x2.
I'm reviewing Meirovitch's "Methods of Analytical Dynamics," and I don't understand the commutation of the derivative from r to dr:
$$
\mathbf{F} \cdot d\mathbf{r} = m \ddot{\mathbf{r}} \cdot d\mathbf{r} = m\mathbf{\dot{r}} \cdot d\mathbf{\dot{r}}
$$