\[\boxed{\text{235\ (235).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ 3x + 7 = (9 + x) + 2x\]
\[3x + 7 = 9 + x + 2x\]
\[3x - 3x = 9 - 7\]
\[0x = 2 \Longrightarrow неверно\ при\ \]
\[любом\ \text{x.}\]
\[Ответ:\ корней\ нет.\]
\[\textbf{б)}\ 5x - 1 = 4 \cdot (x + 2) - (9 - x)\]
\[5x - 1 = 4x + 8 - 9 + x\]
\[5x - 5x = - 1 + 1\]
\[0x = 0 \Longrightarrow верно\ при\ любом\ x.\]
\[Ответ:x - любое\ число.\]
\[\textbf{в)}\ x^{2}\ = x\]
\[x^{2} - x = 0\]
\[x(x - 1) = 0\]
\[x = 0;\ \ \ \ \ x = 1.\]
\[Ответ:x = 0;\ \ x = 1.\]
\[\textbf{г)}\ x + 1 = x - 1\]
\[x - x = - 1 - 1\]
\[0x = - 2 \Longrightarrow неверно\ при\ \]
\[любом\ x.\]
\[Ответ:\ корней\ нет.\]