{(3x+2y)(3x-2y)-(x+2y)(5x-2y)}/8x
={9x^2-4y^2-(5x^2-2xy+10xy-4y^2)}/8x
={4x^2-8xy}/8x
=1/2x-y
=1/2(x-2y)
又因为x-2y=2008
所以=1004