化简cosa^2/sin2a-(1/4)*(cota/2)
问题描述：
化简cosa^2/sin2a-(1/4)*(cota/2)
答
=cos^2a/(2sinacosa)-1/4*(1+cosa)/sina
=cosa/(2sina)-(1+cosa)/(4sina)
=(2-1-cosa)/(4sina)
=(1-cosa)/(4sina)
=tan(a/2)/4