(a^2-b^2+2b-1)/(a^2-b^2+a+b)
=[a^2-(b-1)^2]/[(a-b)(a+b)+a+b]
=(a-b+1)(a+b-1)/[(a+b)(a-b+1)]
=(a+b-1)/(a+b)
=(2005-1)/2005
=2004/2005
(a^2-b^2+2b-1)/(a^2-b^2+a+b)
=[a^2-(b-1)^2]/[(a-b)(a+b)+a+b]
=(a-b+1)(a+b-1)/[(a+b)(a-b+1)]
=(a+b-1)/(a+b)
=(2005-1)/2005
=2004/2005