若X+Y+Z=30,3X+Y-Z=50,X,Y,Z均为非负数,求M=5X+4Y+2Z的取值范围.最后一步不懂

若x+y+z=3y=2z,则x/x+y+z=? (x+y-z)(x-y+z)= 若(x+y)/z=(y+z)/x=(x+z)/y 求（x+y-z)/(x+y+3z)的值 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) 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) 若|x+3|+|y-2|+|2×z+1|=0求(x×z-y×z)(y-x+z)的值 X+Y+Z=? x/y=(x+z)/(y+z)y/z=(x+y)/(x+z) 若x+y+z=30,3x+y-z=50,x,y,z均为非负数若X+Y+Z=30,3X+Y-Z=50,X,Y,Z均为非负数,求M=5X+4Y+2Z的取值范围.很多人做出来都是120 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