- a) Для уравнения $$2x^2 + 5x - 7 = 0$$: $$a = 2$$, $$b = 5$$, $$c = -7$$.
- б) Для уравнения $$x^2 - 8x + 4 = 0$$: $$a = 1$$, $$b = -8$$, $$c = 4$$.
- в) Для уравнения $$-x^2 + x - 1 = 0$$: $$a = -1$$, $$b = 1$$, $$c = -1$$.
Ответ: a) a = 2, b = 5, c = -7; б) a = 1, b = -8, c = 4; в) a = -1, b = 1, c = -1