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=...

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=... (x^2)dy+（y^2)dx=dx-dy 微分方程(x+y)(dx-dy)=dx+dy的通解 y'=dy和y'=dy/dx和dy''=dy'/dx哪个是对的? dy/dx=x+y 求微分方程的通解：x^2(d^2y/dx^2)=(dy/dx)^2+2x(dy/dx) dy/dx-y/x=x^2 参数方程的二阶导数中d^2y/dx^2=(d/dx)(dy/dx)=(d/dt)(1/dx/dt)(dy/dx),是一个 微分方程 dy/dx=(-2x)/y 请解释下微积分中dx,dy的含义,dx和dy是指x=...和y=...的式子吗（比如参数方程）?还是x的导数和y的导数. d(x+y)=dx+dy, y=[sin(x^4)]^2,则dy/dx=?,dy^2/dx^2=?,dy/d(x^2)=?