1. The problem statement, all variables and given/known data Let C be a regular curve enclosing the distinct points w1,..., wn and let p(w)= (w-w1)(w-w2)...(w-wn). Suppose that f(w) is analytic in a region that includes C. Show that P(z)= (1/2[itex]\pi[/itex]i)∫(f(w)[itex]\div[/itex]p(w))[itex]\times[/itex]((p(w)-p(z)[itex]\div[/itex](w-z))[itex]\times[/itex]dw is a polynomial of degree n-1 with P(wk) = f(wk), k= 1,2,... 2. Relevant equations 3. The attempt at a solution So far I know this has something to do with the argument principle and possibly the residue theorem. I believe the inside of the integral reduces to (p'(w)[itex]\div[/itex]p(w))[itex]\times[/itex]f(w)dw, which is why I think the argument principle pertains to this problem. After this I am not sure what to do. This problem is from Bak and Newman Complex Analysis, third edition, chapter 10, if anyone is familiar with the book.