(说明:考虑到难易程度,未按题目所给次序解题)
(1)1/x+1/y+1/z=(xy+yz+xz)/xyz=-1/2
(2)x^2+y^2+z^2=(x+y+z)^2-2(xy+yz+xz)=9+2=11
(3)(2+x)(2+y)(2+z) =8+4(x+y+z)+2(xy+yz+xz)+xyz=8+12-2+2=20
(4)x^3+y^3+z^3
=(x+y+z)^3-3xy(x+y)-3yz(y+z)-3zx(z+x)-6xyz
=27-3xy(3-z)-3yz(3-x)-3zx(3-y)-12
=15-9xy+3xyz-9yz+3xyz-9zx+3xyz
=15-9(xy+yz+xz)+9xyz
=15+9+18=42