(a)

(b) since , for any close loop not enclosing 0, we have

so we can define , where is fixed and the line integral goes on any curve that not crossing 0.

Choose , and the curve from (1, 0) to p(x0,y0) be from (1,0) to (x0,0), then from (x0, 0) to (x0,y0)

we get

=