已知x+y+z=0,xyz=1,求证：x,y,z中必有一个大于2/3.

已知x,y,z>0,xyz(x+y+z)=1,求证（x+y）(x+z)>=2 已知x+y+z=0求证x*x*x+y*y*y+z*z*z=3xyz 已知X+Y+Z=0,求证X^3+Y^3+Z^3=3XYZ 已知：x+y+z=0,求证：x^3+y^3+z^3=3xyz 已知:x+y+z=0,求证x^3+y^3+z^3=3xyz 已知x^2+y^2+z^2=1,求证x+y+z-2xyz 已知（x+y)(y+z)(z+x)=0,xyz不等于0 求证：1/x+1/y+1/z=1/(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=0,xyz=1,求证：x,y,z中必有一个大于2/3. 已知xyz满足z+y+z=xyz 求证：x(1-y2)(1-z2)+y(1-x2)(1-z2)+z(1-x2)(1-y2)=4xyz 已知 (x+y-z)/z=(x-y+z)/y=(y+z-x)/x,且xyz≠0,求代数式 ((x+y)(y+z)(x+z))/xyz 已知：x+y+z=0.求证：x三次+y上次+z三次=3xyz. 已知x,y,z满足xyz=1,求证x^3/(x+y)+y^3/(y+z)+z^3/(z+x)大于等于3 已知x,y,z都是正数,且xyz=1,求证：x^2/(y+z)+y^2/(x+z)+z^2/(x+y)≥3/2 已知：x+y+z=0,求证：x³+y³+z=3xyz.已知：x+y+z=0,求证：x³+y³+z³=3xyz. 已知x、y、z满足x+y+z=xyz,求证：x(1-y^2)(1-z^2)+y(1-x^2)(1-z^2)+z(1-x^2)(1-y^2)=4xyz 已知X+Y+Z=0,求（X+Y)(Y+Z)(X+Z)+XYZ的值. 已知x+y+z=0,求(x+y)(y+z)(z+x)+xyz的值