x-z=4,2y-z=1,x+y+z=-1求xyz的值
问题描述：
x-z=4,2y-z=1,x+y+z=-1求xyz的值
答
x-z=4可得：x=z+4
2y-z=1可得：y=(z+1)/2
代入x+y+z=-1
得：z+4+(z+1)/2+z = -1
2z+8+z+1+2z= -2
5z= -11
z= -11/5
x= -11/5+4= 9/5
y= (-11/5+1)/2= -3/5