Question

Знайдіть число 7993•  7991 – 2009• 2007 (без калькулятора).

Answer 1

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

Answer 2

63872063-4032063=59840000