答案是:7056114
2007^2+2009^2-(2008/2)^2
=2007^2+2009^2-(1004)^2
=2007^2+2009^2-1008016
(用完全平方,配方.A^2-2AB+B^2=(A+B)^2,而2*2007*2009=8064126.
又-1008016=-8064126+7056110)
=2007^2-2*2007*2009+2009^2+7056110
=（2007-2009)^2+7056110
=4+7056110
=7056114