y=sin(x+y).两边对x求导得：
y’=cos(x+y)(1+y')
y'=cos(x+y)/(1-cos(x+y))
所以：dy=[cos(x+y)/(1-cos(x+y))]dxy'=cos(x+y)/(1-cos(x+y))这步怎么弄的从y’=cos(x+y)(1+y')解出y'能说详细点不怎么啦？解一次方程？y’=cos(x+y)(1+y')=cos(x+y)+y'cos(x+y)y'(1-cos(x+y))=cos(x+y)y'=cos(x+y)/(1-cos(x+y))