\[\boxed{\text{681\ (681).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[4x^{2} + bx + c = 0,\]
\[\text{\ \ }x_{1} = 0,5,\ x_{2} = c\]
\[x^{2} + \frac{b}{4}x + \frac{c}{4} = 0\]
\[- \frac{b}{4} = 0,5 + 0\ \ \ \ \ | \cdot ( - 4)\]
\[b = - 2\]
\[Ответ:b = - 2,\ c = 0\text{.\ }\]