Решебник по математике 6 класс Виленкин Часть 1, 2 Часть 2. Задачи на повторение 31

\[\boxed{\mathbf{П.\ 31}}\]

\[1)\ 7 \cdot (x - 4) - 7 = 8 \cdot (x - 4)\]

\[7x - 28 - 7 = 8x - 32\]

\[7x - 8x = - 32 + 35\]

\[- x = 3\]

\[x = - 3.\]

\[2)\ 6 \cdot (x - 7) + 13x =\]

\[= 7 \cdot (2x - 6) + 27\]

\[6x - 42 + 13x = 14x - 42 + 27\]

\[19x - 14x = 27 - 42 + 42\]

\[5x = 27\]

\[x = 27\ :5\]

\[x = 5,4.\]

\[3)\ (1,3y - 5,9) \cdot ( - 3,5) =\]

\[= 6,8y - 11,13\]

\[- 4,55y + 20,65 = 6,8y - 11,13\]

\[- 4,55y - 6,8y =\]

\[= - 11,13 - 20,65\]

\[- 11,35y = - 31,78\]

\[y = 2,8.\]

\[4)\ 1,2 \cdot (z - 2,1) =\]

\[= 1,3 \cdot (z - 1,6) - 0,52\]

\[1,2z - 2,52 = 1,3z - 2,08 - 0,52\]

\[1,2z - 1,3z = - 2,6 + 2,52\]

\[- 0,1z = - 0,08\]

\[z = 0,08\ :0,1\]

\[z = 0,8.\]