已知x:y:z=2:3:5且2x-y+z= -18.求：x+2y-z的值.

已知xyz不等于0,且{x+3y+5z=0 x2+3y+z=0,则x.x+y.y-2z.2z/3x.3x+2y.2y+z.z=? 已知x-y/x+y=y+z/2(y-z)=z+x/3(z-x),求证8x+9y+5z=0THX.. 已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 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+z-y=36求x+y+z的值 已知x:y:z=2:3:4,且x+z-y=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. 已知x,y,z满足方程组x-2y+z=0 7x+4y-5z=0,且z不等于0,2x²-3y²+z²/y²-2z²的值为? thank you已知x+3y+5z=0,2x+3y+z=0 且x、y、z.都不是0,则（2y-z）（2y+z）除以z的平方等多少? 已知x=y/3=z/5.且x+y-2z不等于0.求2x+3y-z/x+y-2z的值是多少 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/2=y/3=z/4,且x+y+z不等于0,求2x+3y-4z/x+y+z的值 已知方程组{2x-3y+z=0 且x*y*z不等于0 求 x：y：z {3x-2y-6z=0 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/2=Y+Z/3=Z+X/4,且2X+4Y+6Z=120,求X,Y,Z的值 已知x+y/2=y+z/3=x+z/4 且2x+4y+6z=120,求x、y、z的值 设|x|-|y|+|z|=|x+y+z|,且|x+y|=4,|y+z|=5,|y|=3,求(x-y-z)^2的值