１.x+y+z=5,y+z=7,求x的值,说明根据等式的什么性质.２.已知:方程x=10

(y+z)/x=(z+x)/y=(x+y)/z求x+y-z/x+y+z的值 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. 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:x+y+z=0,5x-3y-z=0,求:5x-y+z/2x+8y+7z 的值 已知x、y、z满足{3x+7y+z=5 ,求x+y+z的值 {4x+10y+z=3 已知x,y,z满足3x+7y+z=5 4x+10y+z=3 求x+y+z的值 已知x+4y+3z=3x-2y-5z=0,求x+2y-z/2x-3y+7z的值 已知x.y.z满足x-2y+z=0且7x+4y-5z=0,求x:y:z的值 已知5分之X+Y=6分之Y+Z=7分之x+z,且X,Y,Z都不等于0,求X:Y:Z的值 已知：(x+y)/5=(y+z)/6=(x+z)/7,且x*y*z不等于零,求x:y:z的值. 已知x,y,z满足方程组x-2y+z=0 7x+4y-5z=0求x:y:z的值 已知x、y、z满足{x-2y+z=0;7x+4x-5z=0,求x:y:z的值. 已知3x=5y,4y=5z求：1.z的值2.x：y：z 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 已知x+y+z=0,求(x+y)(y+z)(x+z)+xyz的值 x+y-z=3 y+z-x=5 z+x-y=7 求x,y,z 若x,y,z,满足3x+2y+z=5,2x+y-3z=1.y是非负数.求z的取值范围