y=sin(x+y) 求dy/dx
问题描述：
y=sin(x+y) 求dy/dx
还有一个arctan y/x =x/y 求导数
答
y=sin(x+y)
dy=cos(x+y)(dx+dy)
dy=cos(x+y)dx+cos(x+y)dy
dy/dx=cos(x+y)/(1-cos(x+y))