[tex]\it f(x)=ax+b\ \ \ \ \ (*)\ \ \ (forma\ general\breve a\ a\ func\c{\it t}iei)\\ \\ A(2,\ 8)\in Gf\ \Rightarrow f(2)=8\ \stackrel{(*)}{\Longrightarrow}\ 2a+b=8\ \Rightarrow b=8-2a\ \ \ \ \ (1)\\ \\ B(-1,\ -7)\in Gf\ \Rightarrow f(-1)=-7\ \stackrel{(*)}{\Longrightarrow}\ -a+b=-7\ \Rightarrow b=-7+a\ \ \ \ \ (2)[/tex]
[tex]\it (1),\ (2) \Rightarrow -7+a=8-2a \Rightarrow a+2a=8+7 \Rightarrow 3a=15 \Rightarrow a=5\ \ \ \ \ (3)\\ \\ (1),\ (3) \Rightarrow b=8-2\cdot5=8-10=-2\\ \\ Prin\ urmare,\ \ f(x) =5x-2[/tex]
