（1）cos(π/5)+cos(2π/5)+cos(3π/5)+cos(4π/5)　　=cos(π/5)+cos(2π/5)-cos(2π/5)-cos(π/5)　　=0（2）tan10°+tan170°+sin1866°-sin(-606°）　　=tan10°+tan（180°-10°）+sin（5*360°+66°）-sin(-3...