Bài 2:
c) \(f\left(1\right)-f\left(0\right)=2.0-3=-3\)
\(\Rightarrow a+b+c-c=-3\Rightarrow a+b=-3\) (1)
\(f\left(2\right)-f\left(1\right)=2.1-3=-1\)
\(\Rightarrow4a+2b+c-\left(a+b+c\right)=-1\)
\(\Rightarrow3a+b=-1\) (2)
-Từ (1) và (2) suy ra: \(a=1;b=-4\)
\(\dfrac{f\left(5\right)-f\left(2\right)}{9}=\dfrac{25a+5b+c-\left(4a+2b+c\right)}{9}=\dfrac{21a+3b}{9}=\dfrac{7a+b}{3}=\dfrac{7.1-4}{3}=1\)