绝对值非负,平方非负
所以 3x+1=0.y=1
x=-1/3,y=1
(2x³+3x²)-(x³-3x²-y的2008次方)
=(-2/27+1/3)-(-1/27-1/3-1)
=-1/27 +2/3 +1
=1又17/17