Question

利用三角函数的单调性，比较下列各组中两个三角函数值的大小： (3)cos515°与cos530°

利用三角函数的单调性，比较下列各组中两个三角函数值的大小：
(3)cos515°与cos530° (4)sin(-54/7π)与sin(-63/8π)

Answer 1

详细答案见:http://tieba.baidu.com/p/1411147013

Answer 2

cos515° = cos155° = - cos25°
cos530° = cos170° = - cos10°
- cos25° > - cos10°

sin(-54π/7) = -sin(54π/7) = sin(2π/7)
sin(-63π/8) = -sin(63π/8) = sin(π/8)
sin(2π/7) > sin(π/8)