1.负数；
2.sin(-17π/5)=-sin(17π/5),负数.
3.负数.
4.cos(-23π/4)=cos(23π/4)=cos(6π-（π/4））=cosπ/4.正数.
5.cos940°=cos(720+220)=cos(180+40)=cos40º,正数.
6.cos（-59π/17)＝cos59π/17＝cos(2π+π+(8π/17))＝－cos8π/17,负数.