dz/dx=əz/əx+(əz/əy)×(dy/dx)=1/[1+(x/y)²]×(1/y)+[1+(x/y)²]×(-x/y²)×x/√(x²+1)=[y-x²/√(x²+1)]/(x²+y²) =1/[(2x²+1)√(x²+1)] 或者...