MathDB
Putnam 1987 B4

Source:

August 5, 2019
Putnam

Problem Statement

Let (x1,y1)=(0.8,0.6)(x_1,y_1) = (0.8, 0.6) and let xn+1=xncosynynsinynx_{n+1} = x_n \cos y_n - y_n \sin y_n and yn+1=xnsinyn+yncosyny_{n+1}= x_n \sin y_n + y_n \cos y_n for n=1,2,3,n=1,2,3,\dots. For each of limnxn\lim_{n\to \infty} x_n and limnyn\lim_{n \to \infty} y_n, prove that the limit exists and find it or prove that the limit does not exist.