当a=-1,b=2分之1
2(a-2b)^2-3(2a+b)+5(a-2b)^2-(b+2a)
＝7（a-2b)^2-4(b+2a)
=7(-1+1)^2-4(1/2-2)
=-4(-3/2)
=6
当x=-2007,y=2008时,
多项式7x^3-6x^3y+3x^2y+3x^3+6x^3y-3x^2y-10x^3
=(7x^3+3x^3-10x^3)+(-6x^3y+6x^3y)+(3x^2y-3x^2y)
=0+0+0
=0