Вопрос пользователя:
(7n-3)^2 – (7n+1)(7n-1)
Илюха отвечает:
(7n-3)^2 – формула (а-в)^2=a^2-2aB+B^2
(7n-3)^2=(7n)^2-2*7n*3+3^2=49n^2-42n+9
(7n+1)(7n-1) – формула (а-в)(а+в)=a^2-в^2
(7n+1)(7n-1)=49n^2-1
(7n-3)^2 – (7n+1)(7n-1)=49n^2-42n+9-(49n^2-1)=49n^2-42n+9-49n^2+1=-42n+10