\[\boxed{\text{661\ (661).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ x^{2} + 8x = 0\]
\[x(x + 8) = 0\]
\[x = 0\ \ или\ \ x + 8 = 0\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = - 8\]
\[Ответ:x = 0;\ \ x = - 8.\]
\[\textbf{б)}\ 5x^{2} - x = 0\]
\[x(5x - 1) = 0\]
\[x = 0\ \ или\ \ 5x = 1\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = \frac{1}{5} = 0,2\]
\[Ответ:x = 0;\ \ x = 0,2.\]
\[\textbf{в)}\ 6y^{2} - 30y = 0\]
\[6y(y - 5) = 0\]
\[y = 0\ \ \ или\ \ \ \ y - 5 = 0\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ y = 5\]
\[Ответ:y = 0;\ \ y = 5.\]
\[\textbf{г)}\ 3x^{2} - 1,2x = 0\]
\[1,2x(2,5x - 1) = 0\]
\[x = 0\ \ или\ \ \ 2,5x = 1\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = 0,4\]
\[Ответ:x = 0;\ \ x = 0,4.\]
\[\textbf{д)}\ 6x^{2} - 0,5x = 0\]
\[0,5x(12x - 1) = 0\]
\[x = 0\ \ или\ \ \ \ 12x - 1 = 0\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = \frac{1}{12}\]
\[Ответ:x = 0;\ \ x = \frac{1}{12}.\]
\[\textbf{е)}\ \frac{1}{4}y^{2} + y = 0\]
\[y\left( \frac{1}{4}y + 1 \right) = 0\]
\[y = 0\ \ \ \ или\ \ \ \frac{1}{4}y = - 1\]
\(y = - 4\)
\(Ответ:y = 0;\ \ y = - 4.\)
\[\textbf{ж)}\ x - 10x^{2} = 0\]
\[x(1 - 10x) = 0\]
\[x = 0\ \ или\ \ 1 = 10x\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = 0,1\]
\[Ответ:x = 0;\ \ x = 0,1.\]
\[\textbf{з)}\ 6x - 0,2x^{2} = 0\]
\[x(6 - 0,2x) = 0\]
\[x = 0\ \ или\ \ \ \ 6 = 0,2x\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x = 30\]
\[Ответ:x = 0;\ \ x = 30.\]
\[\textbf{и)}\ \ y^{2} + \frac{2}{3}y = 0\]
\[y\left( y + \frac{2}{3} \right) = 0\]
\[y = 0\ \ \ \ \ или\ \ \ \ y = - \frac{2}{3}\]
\[Ответ:y = 0;\ \ y = - \frac{2}{3}.\]