ГДЗ по алгебре 7 класс Макарычев ФГОС Задание 842

\[\boxed{\text{842.}\text{\ }еуроки - ответы\ на\ пятёрку}\]

\[\textbf{а)}\ (x + 1)^{2} - (x - 3)^{2} = 120\]

\[x^{2} + 2x + 1 - \left( x^{2} - 6x + 9 \right) = 120\]

\[x^{2} + 2x + 1 - x^{2} + 6x - 9 = 120\]

\[8x = 120 + 8\]

\[8x = 128\]

\[x = 16\]

\[Ответ:при\ x = 16.\]

\[\textbf{б)}\ (2x + 10)^{2} = 4 \cdot (x - 5)²\]

\[4x^{2} + 40x + 100 = 4 \cdot \left( x^{2} - 10x + 25 \right)\]

\[4x^{2} + 40x + 100 = 4x^{2} - 40x + 100\]

\[4x^{2} + 40x + 100 - 4x^{2} + 40x - 100 = 0\]

\[80x = 0\]

\[x = 0\]

\[Ответ:при\ x = 0.\]