[tex]\it f(x)=ax^2+x+c\ \ \ \ \ \ (1)\\ \\ B(0,\ 3)\in Gf \Rightarrow f(0)=3 \Rightarrow a\cdot0+0+c=3 \Rightarrow c=3\\ \\ c=3 \stackrel{(1)}{\Longrightarrow} f(x)=ax^2+x+3\ \ \ \ \ (2)\\ \\ A(1,\ 2) \in Gf \Rightarrow f(1)=2 \Rightarrow a\cdot1+1+3=2 \Rightarrow a+4=2|_{-4} \Rightarrow a=-2[/tex]
[tex]\it a=-2 \stackrel{(2)}{\Longrightarrow} f(x)=-2x^2+x+3\ \ \ \ \ (3)[/tex]
