Решебник по алгебре 7 класс Мерзляк ФГОС Задание 979

 

\[\boxed{\text{979\ (979).\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[1)\ P = 2 \cdot (a + b)\]

\[2 \cdot (x + y) = 18\ \ \ |\ :2\]

\[x + y = 9\]

\[2)\ 4x + 3y = 250\]

\[3)\ 2y - 5x = 12\]

\[4)\ 0,12x + 0,2y = 9\]

\[5)\ x - 8 = y + 8\]

\[x - y = 16\]

\[\boxed{\text{979.\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

\[f(x) = 3 + 4x\]

\[1)\ f(x) = 19:\]

\[3 + 4x = 19\]

\[4x = 16\]

\[x = 4.\]

\[2)\ f(x) = - 3:\]

\[3 + 4x = - 3\]

\[4x = - 6\]

\[x = - 1,5.\]

\[3)\ f(x) = 0:\]

\[3 + 4x = 0\]

\[4x = - 3\]

\[x = - \frac{3}{4} = - 0,75.\]

\[4)\ f(x) = 323\]

\[3 + 4x = 323\]

\[4x = 320\]

\[x = 80.\]