am=sin1/2+sin2/2^2+……+sinn/2^n+sin(n+1)/2^(n+1)+……+sinm/2^m
an=sin1/2+sin2/2^2+……+sinn)/2^n
所以
|am-an|
=|sin(n+1)/2^(n+1)+……+sinm/2^m|
≤|(sin(n+1))/2^(n+1)|+……+|sinm/2^m|