Ta có:
+ a = 2
+ $ - \dfrac{b}{{2a}} = 1 \Leftrightarrow 2a + b = 0$ $\Leftrightarrow 4 + b = 0 \Leftrightarrow b = - 4$
+ $ - \dfrac{\Delta }{{4a}} = 4 \Leftrightarrow \dfrac{{ - {b^2} + 4ac}}{{4a}} = 4 \Leftrightarrow - {b^2} + 4ac = 16a\\ \Leftrightarrow - {b^2} + 8c = 32 \Leftrightarrow - {\left( { - 4} \right)^2} + 8c = 32 \Leftrightarrow c = 6 $
Vậy $a = 2, b =-4,c=6$