已知x,y,z∈R^+,x+y+z=xyz,且去1/(x+y)+1/(y+z)+1/(z+x)≤k恒成立,则k的取值范围是?

已知x,y,z∈R,求证:x^2+y^2>=xy+x+y-1 已知x,y,z∈R+,且x+y+z=3,求证：x^2/（y^2+z^2+yz）+y^2/(x^2+z^2+zx）+z^2/(x^2+y^2+xy)≥1 不等式计算已知x、y、z∈R+,且x^2+y^2+z^2=1,则yz/x+zx/y+xy/z的最小值是 已知x,y∈R,且1≤x^2+y^2≤2,z=x^2+xy+y^2,则z的取值范围是 已知x+y+yz=5,y+z+xy=8,x+z+xy=9,求x,y,z 已知x,y,z∈ R,x+2y=z+6,x-y=3-2z,求x^2+y^2+z^2的最小值. 求全微分函数Z(X,Y),已知方程 Z^2*ln（X+Z)=XY 已知XY=2(X+Y),YZ=4(Y+Z),ZX=5(Z+X),求X,Y,Z已知XY=2(X+Y),YZ=4(Y+Z),ZX=5(Z+X),求X,Y,Z 已知x-y=6,xy=-8,求代数式½(x+y+z)²+½(x-y-z)(x-y+z)-z(x+y) 已知x、y、z∈R+,xyz=1,求证：x/(1+xy)+y/(1+yz)+z/(1+zx)≥3/2. 求教已知x、y、z∈R+,且 [根号下(x^2+y^2)] + z=1,则xy+2xz的最大值为______. 证明 已知xyz∈R^+, x^2x * y^2y* z^2z≥x^y+x* y^z+x * z^x+y x y z∈R+且x+y+z=1求（yz/x）+（xz/y）+（xy/z）的最小值. 已知X+Y+Z=a,XY+YZ+XZ=b,求X*X+Y*Y+Z*Z的值 已知实数x,y,z,满足那么x+y=6,z^2=xy-9,求(x+y)^z 已知x,y,z>0 求证:xy(x+y)+yz(y+z)+zx(z+x)>=6xyz 已知 x/(y+z)+y/(z+x)+z/(x+y)=1求 (x*x)/(y+z)+(y*y)/(x+z)+(z*z)/(x+y)=? 已知x、y、z∈R＋,求证x⒋+y⒋+z⒋≥(x+y+z)xyz