1.x+y+z=30,3x+y-z=50,x,y,z为非负数,求5x+4y+2z取值范围.2.（2a-b)x+3a-4b4/9,求(a-4b)x+2a-3b>0 的解集3.若x1,x2都满足|2x-1|+|2x+3|=4,x1

(x+y-z)(x-y+z)= 已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 试证明(x+y-2z)+(y+z-2x)+(z+x-2y)=3(x+y-2z)(y+z-2x)(z+x-2y) X+Y+Z=? x/y=(x+z)/(y+z)y/z=(x+y)/(x+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)=? x+y-z=3 y+z-x=5 z+x-y=7 求x,y,z 已知x+y+z=0求证x*x*x+y*y*y+z*z*z=3xyz 证明 ：x/(y+z)+y/(z+x)+z/(x+y)>=3/2其中 x,y,z>0 (y+z)/x=(z+x)/y=(x+y)/z求x+y-z/x+y+z的值 x+y+z=30 3x+2y+z=50求详解 x/2=y/3=z/5 x+3y-z/x-3y+z x+y/2=z+x/3=y+z/4 x+y+z=27 若x+y+z=3y=2z,则x/x+y+z=? x+2y=3x+2z=4y+z 求x:y:z 6x+5y+3z=100 x+y+z=30 求 x y 急 x,y,z均为正整数,x>=y,y>=z,z>=8 x+3y-z=急x,y,z均为正整数,x>=y,y>=z,z>=8x+3y-z=132,请问1.x+y+z有最小值782.x+y+z有最大值1343.洽有一组解(x,y,z)使得x+y+z有最大值4.x+3y有最小值1405.x+2y有最大值130 解下列三元一次方程组：1.{x：y：z=1：2：3,2x+y-3z=152.{2x+y+z=-26,x+2y+z-30,x+y+2z=-28.