Well, that is correct because the left-limit is not equal to the right limit. In deed the function y = 0 is the vertical asypmtote of this given function. The left limit is the negative infinity and the right limit is the positive infinity. One can prove this by making a sign chart of the function 1/X
I'm reviewing Meirovitch's "Methods of Analytical Dynamics," and I don't understand the commutation of the derivative from r to dr:
$$
\mathbf{F} \cdot d\mathbf{r} = m \ddot{\mathbf{r}} \cdot d\mathbf{r} = m\mathbf{\dot{r}} \cdot d\mathbf{\dot{r}}
$$