ГДЗ по алгебре 7 класс Макарычев ФГОС Задание 989

\[\boxed{\text{989.}\text{\ }еуроки - ответы\ на\ пятёрку}\]

\[\textbf{а)}\ (a + 2)(a - 2) - a(a - 5) =\]

\[= \left( a^{2} - 4 \right) - a^{2} + 5a =\]

\[= a^{2} - 4 - a^{2} + 5a =\]

\[= 5a - 4\]

\[\textbf{б)}\ (a - 3)(3 + a) + a(7 - a) =\]

\[= \left( a^{2} - 9 \right) + 7a - a^{2} = a^{2} -\]

\[- 9 + 7a - a^{2} =\]

\[= 7a - 9\]

\[\textbf{в)}\ (b - 4)(b + 4) -\]

\[- (b - 3)(b + 5) = b^{2} - 16 -\]

\[- \left( b^{2} + 5b - 5b - 15 \right) =\]

\[= b^{2} - 16 - b^{2} - 5b + 3b +\]

\[+ 15 = - 2b - 1\]

\[\textbf{г)}\ (b + 8)(b - 6) -\]

\[- (b - 7)(b + 7) = b^{2} - 6b +\]

\[+ 8b - 48 - b^{2} + 49 =\]

\[= 2b + 1\]

\[\textbf{д)}\ (c - 1)(c + 1) +\]

\[+ (c - 9)(c + 9) = c^{2} - 1 +\]

\[+ c^{2} - 81 = 2c^{2} - 82\]

\[\textbf{е)}\ (5 + c)(c - 5) -\]

\[- (c - 10)(c + 10) = c^{2} - 25 -\]

\[- c^{2} + 100 = 75\]