x/2=y/3=z/0.5
得x=4z,y=6z
2X-Y+Z分之X+3Y-Z
=8z-6z+z分之4z+18z-z
=3z分之21z
=7
选择B
2、
a²+b²=6ab
(a+b)²-2ab=6ab,（a+b)=±√8ab
(a-b)²+2ab=6ab,（a-b)=±√4ab
a-b分之a+b=±√8ab/±√4ab=±√2
因a>b>0,所以取正值
选择A