高数高数
高数dz=2xdx+2ydy2xdx-ydx-xdy+2ydy=0(x-2y)dy=(2x-y)dxdy=(2x-y)dx /(x-2y)∴dz=2xdx+2y(2x-y)dx /(x-2y)dz/dx=2x+2y(2x-y)/(x-2y)=(2x^2-2xy+4xy-2y^2)/(x-2y)=(2x^2+2xy-2y^2)/(x-2y)