$c = 0$: маємо рівняння $ax^2 + bx = 0 \Longleftrightarrow x\cdot(ax + b) = 0 \Longleftrightarrow \left[ \begin{gathered} x = 0,\\ ax + b = 0; \end{gathered} \right.$ $\Longleftrightarrow \left[ \begin{gathered} x_1 = 0,\\ x_2 = -\dfrac{b}{a}. \end{gathered} \right.$
Наприклад: $6x^2 - x = 0 \Longleftrightarrow x\cdot(6x - 1) = 0 \Longleftrightarrow \left[ \begin{gathered} x = 0,\\ 6x - 1 = 0; \end{gathered} \right. \Longleftrightarrow \left[ \begin{gathered} x_1 = 0,\\ x_2 = \dfrac{1}{6}. \end{gathered} \right.$