将下列三角函数化为0到π/4之间角的三角函数:(1)cosπ/3 (2)sin3π/5 (3)sin(-1920°)
问题描述：
将下列三角函数化为0到π/4之间角的三角函数:(1)cosπ/3 (2)sin3π/5 (3)sin(-1920°)
答
（1）cosπ/3=cos(π/2-π/6)=sinπ/6（2）sin(3π/5)=sin(π-2/5π)=sin(2/5π)=sin(π/2-π/10)=cosπ/10（3）1920°=32/3πsin(-1920°)=sin(-32/3π)=-sin(10π+2/3π)=-sin(2/3π)=-sin(π/3)=-cos(π/6)