I have an exercise, I have to determine the Taylor polynomial for second order differential in a certain point for a few functions. The problem is if I compute the second order differential in the given point, I am left with no variables, so I can't apply Taylor for it. Or I'm doing something wrong.
For example for $~f(x,y)=\arctan(x/y),~~~ x>0~$ in point $(1,1)$
I would appreciate if someone could explain a method to solve it or give an example, thank you!