I have to find: I I (over S) (2/(sqrt(1+x2+y2)) dx dy
S is a set of x,y such that 1<=x2 + y2 <=4 and x>=0, y>=0.
I understand that we have a circle here, actually a circle within a circle, and as i see, conditions give me only quarter of that circle, r going from 1 to 2 and having 0 to 1/2pi, right?
I guess i should work somehow with polar form, but how to actually do the integral?
thanks