[tex]f(x)=ax^2+bx+c \\ V(- \frac{b}{2a};- \frac{\Delta}{4a} ) \Rightarrow \left \{ {{- \frac{b}{2a}=1 } \atop {- \frac{\Delta}{4a} = -1 }} \right. \\ a=1 \\ b = m \\ c = n \\ -\frac{m}{2} = 1 \Rightarrow m = -2 \\ \Delta = b^2-4ac=m^2-4n=4-4n=4(1-n) \\ - \frac{\Delta}{4a}=-1 \Leftrightarrow - \frac{4(1-n)}{4}=-1 \Leftrightarrow 1-n=1 \Leftrightarrow n = 0 \\ f(x)=x^2-2x [/tex]
