7993 * 7991 = (7992+1) * (7992-1) = 7992^2 - 1 2009 * 2007 = (2008+1) * (2008-1) = 2008^2 - 1 Вычитаем 7992^2 - 1 - (2008^2 - 1) = 7992^2 - 2008^2 = = (7992 + 2008) * (7992 - 2008) =10000 * 5984 = 59840000
63872063-4032063=59840000
7993 * 7991 = (7992+1) * (7992-1) = 7992^2 - 1
2009 * 2007 = (2008+1) * (2008-1) = 2008^2 - 1
Вычитаем
7992^2 - 1 - (2008^2 - 1) = 7992^2 - 2008^2 =
= (7992 + 2008) * (7992 - 2008) =10000 * 5984 = 59840000
63872063-4032063=59840000