计算（1）cosπ/5+cos2π/5+cos3π/5+cos4π/5；（2）tan10°+tan170°+sin1866°-sin（-606°）.
问题描述：
计算（1）cosπ/5+cos2π/5+cos3π/5+cos4π/5；（2）tan10°+tan170°+sin1866°-sin（-606°）.
答
1、cos4π/5=-cos(π-4π/5)=-cosπ/5cos3π/5=-cos(π-3π/5)=-cos2π/5cosπ/5+cos2π/5+cos3π/5+cos4π/5=cosπ/5+cos2π/5-cos2π/5-cosπ/5=02、tan10°+tan170°+sin1866°-sin(-606°）=tan10°+tan（180-10...