若|3x+1|与|y+1|^2是互为相反数,
则：|3x+1|+|y+1|²=0
∴|3x+1|=0,|y+1|=0
3x+1=0,y+1=0
x=-1/3,y=-1
(1)xy=(-1/3)×(-1)=1/3
(2)）-x^3-y^100
=(-1/3)^3-1^100
=(-1/27)-1
=-28/27