y趋向0,1-cosy/ siny
问题描述：
y趋向0,1-cosy/ siny
答
上下同乘1+cosy
得
(1-cos^2 y)/(siny(1+cosy))
=sin^2 y/(siny(1+cosy))
=siny/(1+cosy)
=0/2
=0