Prove that the following sequence is Cauchy:
a_n = [a_(n-1) + a_(n-2)]/2 (i.e. the average of the last two), where
a_0 = x
a_1 = y
The Attempt at a Solution
I was trying to use the definition of Cauchy (i.e. |a_m - a_n| < e) by relating a_n - a_(n-1) to a_(n-1) - a_(n-2), but to no avail.