[Degoutant]

Amg thanks for your fast reply! And thanks, I also kind of understood what to do :

so I did this like you said:

f(2) = 0
8a+4b-3(2)+2 = 0
0=8a+4b-4

f(-1)=0
-a+b-3+2=0
-a+b-1 = 0 | +1
-a+b = 1 |+a
b= 1+a

Now I substitued b into 0=8a+4b-4 which will be:
8a+4(1+a)-4
0=8a+4+4a-4
0=12a|:12
a=0

Substitued a into 1+a:
b=1+0 =1

The equation is:
f(x)=x²+3x+2

Is this right? Because it's only 2. Degree polynomial

thanks in advance!