点击放大,荧屏放大再放大:
F(x,y)=Ln(1+x^2+y^2)F`x=2x/(1+x^2+y^2)F`x=1/3F`y=2y/(1+x^2+y^2)F`y=2/3dF(1,2)=F`x Δx+F`y Δy =1/3*0.1+2/3*0.2=1/6