\[\boxed{\text{771\ (771).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ 1,2x^{2} + x = 0\]
\[x(1,2x + 1) = 0\]
\[Ответ:x = 0;\ \ x = - \frac{5}{6}.\]
\[\textbf{б)}\ 1,6x + x^{2} = 0\]
\[x(1,6 + x) = 0\]
\[x = 0\ \ \ или\ \ \ x = - 1,6\]
\[Ответ:x = 0;\ \ x = - 1,6.\]
\[\textbf{в)}\ 0,5x^{2} - x = 0\]
\[x(0,5x - 1) = 0\]
\[Ответ:x = 0;\ \ x = 2.\]
\[\textbf{г)}\ 5x^{2} = x\]
\[5x^{2} - x = 0\]
\[x(5x - 1) = 0\]
\[x = 0\ \ или\ \ \ \ 5x = 1\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = \frac{1}{5} = 0,2\]
\[Ответ:x = 0;\ \ x = 0,2\]
\[\textbf{д)}\ 1,6x^{2} = 3x\]
\[1,6x^{2} - 3x = 0\]
\[x(1,6x - 3) = 0\]
\[Ответ:x = 0;\ \ x = 1\frac{7}{8}.\]
\[\textbf{е)}\ x = x^{2}\]
\[x - x^{2} = 0\]
\[x(1 - x) = 0\ \]
\[x = 0\ \ \ или\ \ \ \ x = 1\ \]
\[Ответ:x = 0;\ \ x = 1.\]