x²y+2xy+3=-18
两边同时对x求导得：
2xy+x²dy/dx+2y+2xdy/dx+0=0
2xy+2y+(x²+2x)dy/dx=0
(x²+2x)dy/dx=-(2xy+2y)
dy/dx=-(2xy+2y)/(x²+2x)2xy+x²dy/dx+2y+2xdy/dx+0=0 这一部不太理解～x²y对x求导为2xy+x²dy/dx2xy对x求导为2y+2xdy/dxsorry我打错了是2xy^32xy³对x求导为2y³+6xy²dy/dx请采纳。x^2y求导不应该是2xydy／dx＋x^2dy/dx不是的，x²y对x求导是(x²)'y+x²y '=2xy+x²y '=2xy+x²dy/dx