x>=0,y>=0.2x+y=6,则u=4x^2+3xy+y^2-6x-3y最小值

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) x>=0,y>=0.2x+y=6,则u=4x^2+3xy+y^2-6x-3y最小值 这是一道数学题：X+Y-1≤0 X-Y+1≥0 Y≥-1 且U(X,Y)=X²+Y²-4X-4Y+8,则U(X,Y)最小值为多少 若x+y-1==0,y>=-1.且u=x^2+y^2-4x-4y+8,则u的最小值? 假设集合U={(x,y)|x∈R,y∈R },A={(x,y)|2x-y+m>0},B={(x,y)|x+y-n x,y>0,且x+2y=1,u=(x+1/x)(y+1/(4y)最小值是: 已知x >0,y>0,x+y=xy,则u=x+4y的取值范围是? x.y都是自然数,且x(x-u)-y(y-x)+12,求x.y得值快1且x(x-y)-y(y-x)=12 求全微分 u=x^y^z 帮忙证明个高数题u=x^2*y^2/(x+y),求证 x*u(x)+y*u(y)=3u U={y|y=log2x,x>1},P={y|y=1/x,x>2},则CuP= y≥0,x^2 +y^2 =3,u=(y+1)/(x+3) ,求u的最值. 设X,Y相互独立,U(0,1),U(-1,1)则X,Y联合概率密度f(x,y)= 已知实数x,y满足4x+3y>=0,则u=x^2+4x+y^2-2y的最小值为? 证明函数u(x,y)=f(y/x^2)*x^n满足x*（∂u/∂x)+2y*(∂u/∂y)=nu 二元函数u(x,y)=f(x)g(y)的充要条件是u(x,y)*u(_xy)=u'(_x)*u'(_y) （5x-6y)(x+y)=0(x不等于y),则y/x=