\[\boxed{\mathbf{643\ (643).\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[ax^{2} + bx = 0\]
\[x(ax + b) = 0\]
\[x = 0,\ \ x = - \frac{b}{a}\]
\[1)\ если\ \ a > 0,\ \ \ b > 0 \Longrightarrow x = 0;\ \ \]
\[x < 0;\]
\[2)\ если\ \ a < 0,\ \ \ b > 0 \Longrightarrow x = 0;\ \ \]
\[x > 0;\]
\[3)\ если\ \ a > 0,\ \ \ b < 0 \Longrightarrow x = 0;\ \ \]
\[x > 0;\]
\[4)\ если\ \ a < 0,\ \ \ b < 0 \Longrightarrow x = 0;\ \ \]
\[x < 0.\]