已知x：y：z=3:4:5,且x+y+z=12,那么x=?,y=?,z=?

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 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) 已知x+y/2=y+z/3=z+x/4,且x+2y+z=12,求x-2y+z的值 已知3x-2y-5z=0,2x-5y+4z=0,且x,y,z均不为0,求3x*x+2y*y+5z*z/5x*x+y*y- 已知3x-2y-5z=0,2x-5y+4z=0,且x,y,z都不为0,求（3x*x+y*y+4z*z）/（5x*x+y* 已知4X=7Y+5Z,2X+Y=Z,那么X:Y:Z的值是? 已知x:y:z=2:3:4,且x-y+z=36,求x+y+z的值. 已知x:y:z=2:3:4,且x+y+z=18,求x,y,z的值 (x+y-z)(x-y+z)= 已知x+y/2=y+z/2=x+z/4,且x+2y+z=12,求x-2y+z 已知x/2=y/3=z/4,且x+y+z不等于0,求2x+3y-4z/x+y+z的值 已知 x,y,z都是正实数,且 x+y+z=xyz 证明 (y+x)/z+(y+z)/x+(z+x)/y≥2(1/x+1