1.sin 2π/5 与 cos 15π/8 2.tan π/7 与 tan 11π/9

1.sin 2π/5 与 cos 15π/8cos 15π/8=cos(3π/2+3π/8)=sin3π/8y=sinx在（-π/2,π/2）是增函数2π/5=16π/40 >3π/8=15π/40,sin 2π/5 >cos 15π/82.tan π/7 与 tan 11π/9=tan( π+2π/9)=tan 2π/9y=tanx在（...