sin6°sin42°sin66°sin78°
=sin6°cos12°cos24°cos48°
=8cos6°sin6°cos12°cos24°cos48°/8cos6°
=4sin12°cos12°cos24°cos48°/8cos6°
=2sin24°cos24°cos48°/8cos6°
=sin48°cos48°/8cos6°
=sin96°/16cos6°
=sin6°/16cos6°
=1/16sin220°+cos250°+sin20°+cos50°还有这一题哇。。sin220°+cos250°+sin20°+cos50°=-sin40-cos70+sin20+cos50=-cos50-sin20+sin20+cos50=0sin^2 20°+cos^2 50°+sin20°+cos50°前面两个sin20+cos50是有平方的呃。。你看提问的原题百度怎么自己会把小2变成大2...