X+2Y=5Y+2Z=8Z+2U=11U+2X=6

X+2Y=5Y+2Z=8Z+2U=11U+2X=6 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) 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+z) 求二阶偏导数σ2u／σxσy 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) 四元一次方程组x+2y=5y+2z=8z+2u=11u+2x+6 u=x(z+y) z=sin(x+y) 求二阶偏导数σ2u／σxσy 四元一次方程的解法y+z+u=1z+u+x=2u+x+y=3x+y+z=4 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 急求设φ(u)二阶可微,z=x/y*φ(u),u=2y-3x,求z'xx,z'xy的答案呀 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? u=ln(1/(x+√（y^2+z^2))),求u对x、u对y、u对z的偏导数,是u=ln(x+√（y^2+z^2))。没有分之1。 如何matlab求解多元方程x,y,z,u]=solve('48.18577=x/[1+(6280000*x*z)^2]+y/[1+(6280000*y*u)^2]','655.3747=x*{6280000*x*z/[1+(6280000*x*z)^2]}+y*{6280000*y*u/[1+(6280000*y*u)^2]}','49.78774=x/[1+(5709085*x*z)^2]+y/[1+(5709085*y*u)^2]','724.7968=x* x大于等于0,y大于等于0,z大于等于0.3x+2y+z=5,2x+y-3z=1,u=3x+y-7z 求u的最值, 求全导数：z=arctan(u+v),u=x^2+y^2, 设z=arctan(x/y) x=u+v y=u-v 验证δz/δu+δz/δv=(u-v)/(u^2+v^2) 设函数f(u)具有二阶导数,而z=f((e^x)*sin(y))满足方程d^2(z)/d^2(x^2)+d^2(z)/d(y^2)=e^(2*x)*z,求f(u).令u=e^x*siny,则z=f(u)∂z/∂x=∂z/∂u*∂u/∂x=f'(u)*e^x*siny=uf'(u),∂²z/∂x²=∂(u