x+y+z=12 x-y+z=2 x-z+y+a=90 x+y+a+z=100,求x y z a

(x+y-z)(x-y+z)= X+Y+Z=? x y z x+y--- = --- = ---- ----y+Z z+x x+y ,求 z 的值 .求 x+y---- 已知x,y,z,a为自然数,且x＜y＜z,1/x+1/y+1/z=a,求x,y,z,a 的值. 已知X,Y,Z,A,为自然数,且X〈Y〈Z,求1/X+1/Y+1/Z=A,求X,Y,Z的值. 已知X+Y+Z=a,XY+YZ+XZ=b,求X*X+Y*Y+Z*Z的值 已知x+y-z/z=x-y+z/y=-x+y+z/x,且xyz不等于0,求分式[(x+y)(x+z)(y+z)]/xyz 若z分之x+y+z=y分之x-y+z=x分之-x+y+z,求xyz分之(x+y)(y+z)(z+x) y+z÷x=Z+X÷y=X+Y÷z,X+Y+Z不等0求X+Y-Z÷X+Y+z值 (x+y-z)/z=(y+z-x)/x=(z+x-y)/y 求(x+y)(y+z)(z+x)/xyz x分之y+z=y分之z+x=z分之x+y(x+y+z不等于0）,求x+y+z分之x+y-z 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)