f(1)+f(7)
=sin(π/6)+sin(7π/6)
=sin(π/6)+sin(π/6+π)
=sin(π/6)-sin(π/6)
=0
同理
f(3)+f(9)=0
f(5)+f(11)=0
也就是说,每6个数之和为0
原式,从1到2011,共有(2011-1)/2+1=1006个数
1006/6=167.4
原式=f(1)+f(3)+f(5)+f(7)
=f(3)+f(5)
=sin(3π/6)+sin(5π/6)
=1+1/2
=3/2