f(n)=sinnπ/4,求f(1)+f(2)+f(3)+……+f(2008)
f(1)=sinπ/4=√2/2
f(2)=sinπ/2=1
f(3)=sin3π/4=√2/2
f(4)=sinπ=0
f(5)=sin5π/4=-√2/2
f(6)=sin3π/2=-1
f(7)=sin7π/4=-√2/2
f(8)=sin2π=0

因为 sinx的周期为2π
所以 sinnπ/4的周期为 2π/(π/4)=8
f(1)+…………+f(8)=0
所以
f(1)+f(2)+f(3)+……+f(2008)
=0+0+0+……+0+0
0