d(x+y)=dx+dy,

d(x+y)=dx+dy, d{cos(x-y)=sin(x-y)(dx-dy)这里dx-dy是什么意思呢? d^2y/dx^2=(dy/dx)'×(dy/dx),另外请解释下dx,dy的含义,dx和dy是指x=...和y=... dy/dx=x+y dx+dy=d(x+y)是什么原理? y=[sin(x^4)]^2,则dy/dx=?,dy^2/dx^2=?,dy/d(x^2)=? 试从dx/dy=1/y'导出：d^2x/dy^2=-y''/（y')^3 题目中关于d[1/y']/dx}*[dx/dy 从(dx)/(dy)=1/y '导出：(d^2x)/(dy^2)=-y''/(y')^3 求微分方程的通解：x^2(d^2y/dx^2)=(dy/dx)^2+2x(dy/dx) 设y=2arctany/x,求dy/dx,dy^2/d^2x. dx/dy=1/y',求d^2x/dy^2 .为什么d^2x/dy^2不等于dx/dy求导?一个是二阶导数,一个是一阶导 d/dx((x^2+y^2)^2)=d/dx(x^2-y^2),求（化简）dy/dx=?