(sin24°cos6°-sin66°sin6°)/(sin21°cos39°-cos21°sin39°)

sin6°sin42°sin66°sin78°=? sin6°sin42°sin66°sin78°= 1.比大小：tan21°和tan31°；2.sin21°和cos21°；3.cos21°和cos22° cos15°sin9°+sin6°/sin15°sin9°—cos6°= 求该题演算过程设a=1/2COS6°-√3/2sin6°,b=2tan13°/1+tan13°,c=√1-cos50°/ 求值:(sin9°+sin6°cos15°)/(cos9°-sin6°sin15°) cos6°cos54°cos66°等于多少? 化简：cos21°+cos22°+cos23°+…+cos289°． 化简sin6°cos24°sin78°cos48° 求值(sin9°cos15°-sin24°)/(sin9°sin15°+cos24°) 计算：sin21°+sin22°+sin23°+…+sin287°+sin288°+sin289°． 计算：sin21°+sin22°+sin23°+…+sin288°+sin289°+sin290°= ___ ．