u=(x-y)^z,z=x^2+y^2,求u对x的偏导数是（x-y）^（x^2+y^2）[ln(x-y).2x(x-y)+x^2+y^2],主要是u里面有x不知道怎么搞,还有在空间坐标系中怎么求点到直线的距离.

已知x/(y+z+u)=y/(z+u+x)=z/(u+x+y)=u/(x+y+z)求(x+y)/(z+u)+(y+z)/(x+u)+(z+u)/(x+y)+(u+x)/(y+z) x/(y+z+u)=y/(z+u+x)=z/(u+y+x)=u(x+y+z)求(x+y)/(z+u)+(y+z)/(y+x)+(z+y)/(x+y)+(u+x)/(z+y) u=x(z+y) z=sin(x+z) 求二阶偏导数σ2u／σxσy 设x+y+z=11求函数u=2x*x+3y*y+z*z的最小值 u=x(z+y) z=sin(x+y) 求二阶偏导数σ2u／σxσy 用行列式的性质证明：y+z z+x x+y x y z x+y y+z z+x =2 z x y z+x x+y y+z y z x 这个怎么证? 四元一次方程的解法y+z+u=1z+u+x=2u+x+y=3x+y+z=4 (x-2y+z)(x+y-2z)分之（y-x)(z-x) + (x+y-2z)(y+z-2x)分之(z-y)(x-y) + (y+z-2z)(x-2y+z)分之（x-z)(y-z)=?第三部分那个是 （y+z-2x)(x-2y+z)分之（x-z)(y-z) 试证明(x+y-2z)+(y+z-2x)+(z+x-2y)=3(x+y-2z)(y+z-2x)(z+x-2y) 已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 已知：x^2/(z+y)+y^2/(x+z)+z^2/(x+y)=0,求x/(z+y)+y/(x+z)+z/(x+y)的值. x^2/(z+y)+y^2/(x+z)+z^2/(x+y)=0,求x/(z+y)+y/(x+z)+z/(x+y)的值 z=f(u) u=x/y,求x*∂z/∂x +y*z∂z/∂y 帮忙求一个全微分u=2sin（x+2y-3z）-（ x+2y-3z ）.z=z（x,y） 四元一次方程组,天啊.、、、、、、x+y+z+u=4x+y-z-u=-2x-y+z-u=0x+y-z+u=2 X+2Y=5Y+2Z=8Z+2U=11U+2X=6 求u=x+y+z,求u在z=2x^2+y^2条件下的极值 方程2U+V+X+Y+Z=3的非负整数解（X,V,U,Y,Z)有几组?