Z OZ ex2.iz=u, u=x+y, v=xy,r ax ay Solution u yr J azaz au az a n-1.x+uhnu…y ax au ax ay ax =(x2+y2)2x2y+y(x2+y2)hn(x2+y2) =w"-1.2y+u"lnu·x ay au ay av ay =(x2+y2)-12xy2+x(x2+y2)hn(x2+y2) K心2. , , , , . 2 2 yz xz ex z u u x y v xy v   设 = = + = 求 Solution. z uv xyxy xv vz xu uz xz   +   =  vu x u u y v v =  +  − 2 ln 1 ( ) [2 ( )ln( )] 2 2 1 2 2 2 2 2 x y x y y x y x y xy = + + + + − yv vz yu uz yz   +   =  vu y u u x v v =  +  − 2 ln 1 ( ) [2 ( )ln( )] 2 2 1 2 2 2 2 2 x y xy x x y x y xy = + + + + −