Can anyone provide me solution to this identity
http://books.google.com/books?id=PJeHprppOLsC&printsec=frontcover&dq=complex+variables&hl=en&ei=rFl7TMj0E4P-8AbNgOGFBw&sa=X&oi=book_result&ct=book-thumbnail&resnum=2&ved=0CDYQ6wEwAQ#v=onepage&q&f=false"
page 10 , problem 20