Find the open interval(s) on which the curve given by the vector-valued function is smooth.
If I follow the book correctly, I get the derivative which is and then after that I have no idea.
In the example problem it shows and list some intervals, but I'm not sure what they're doing or what's going on.
I believe the mathematical meaning is that we end up dividing by within the computation. And to keep it valid we require vectors being smooth for certain theorerms.