请问cos(-2371/5)与cos(-17π/4））的大小?

题目

请问cos(-2371/5)与cos(-17π/4））的大小?
为什么（-2371/5）=（-23π/5）?

答案

cos(-2371π/5)=cos(-474π-π/5)=cos(-π/5)=cos(π/5)
cos(-17π/4)=cos(-4π-π/4)=cos(-π/4)=cos(π/4)
0＜π/5＜π/4＜π/2
cos(π/5)＞cos(π/4)
cos(-2371π/5)＞cos(-17π/4)