已知x+15=y+12=z+5,求x^2+y^2+z^2-xy-xz-yz今晚要

已知x+y-7z=0 x-2y+5z=0(xyz不等于0）,求x+2y-z/y-2x+12z 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. 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+z=6,x^2+y^2+z^2=12,求x,y,z的值 已知{x：y：z=1：2：3,x+y+z=12,求x、y、z的值 已知{x-5y+2z=0 3x-5y-4z=0,求x：y:z 已知2x+5y+4z=6 3x+y-7z=-4求x+y-z 已知x/4=y/5=z/6 求x+y+z/3x-2y+z的值 已知x/4=y/5=z/6,求x+y+z/3x-2y+z的值. 已知x:y:z=1:3:5,求（2x+3y-z)/(x+y-2z)的值 已知X:Y:Z=3:4:5,求4X+3Y-2Z/X+Y+Z的值 已知x:：y：z=3：4：5,(1)求x+y分之z的值；（2）若x+y+z=6,求x,y,z. 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z、y、z同时满足x+3y-5z=0,2x-y-3z=0,求x:y:z 已知x、y、z满足{x-2y+z=0;7x+4x-5z=0,求x:y:z的值. 已知x+y/2=y+z/3=z+x/4,且x+2y+z=12,求x-2y+z的值 已知x+y-z=0,2x-y+2z=0 求（3x-2y+5z)/(5x-3y+2z)的值