2008^2-2007*2008 (1)
=2008(2008-2007)
=2008
3.98^2-3.98*3.97 (2)
=3.98(3.98-3.97)
=0.0398
3ab^2+6a^2+ab (3)
=a(3b^2+6a+b)
a^3(x-y)-3a^2b(y-x) (4)
=(x-y)a^2(a+3b)
=(x-y)(a+3b)a^2
3^2007+6*3^2006-3^2008 (5)
=3*3^2006+6*3^2006-9*3^2006
=3^2006(3+6-9)
=0