arctanyx的精选

偏导为：-2xy/(x²+y²)²解:原式=∂z/∂x=1/(1+y²/x²)*(-y/x²)=-y/(x²+y²)∂z/∂y=1/(1+y²/x²)*1/x=x/(x²+y²)∂²z/∂x²=y/(x²+y²)*2x=2xy/(x²+y²)²∂²z/∂x∂y=-[x²+y²-2y²]/(x²+y²)²=(y²-x...