Question

三角函数 (11 13:39:35)

Answer 1

-π/2＜a＜π/2

-π/2＜b＜π/2

相加

-π＜a+b＜π

-π/2＜b＜π/2

所以-π/2＜-b＜π/2

-π/2＜a＜π/2

相加

-π＜a-b＜π

a＜b

所以a-b＜0

所以-π＜a-b＜0