Bantu aku dong yang ini..please..

f(1)= 2, f(2)=5, f(3)=8
f(x) = ax+b
f(1) = a.1+b
f(1)=a+b=2
2=a+b
2-b=a

f(2)=5
f(x) =ax+b
f(2)=a.2+b
f(2)=(2-b)2+b
f(2)=4-2b+b
5 = 4-2b+b
5 = 4-b
b=4-5
b=-1

menentukan nilai a
a= 2-b
a= 2-(-1)
a= 2+1
a=3

penerapan
f(3)=8
f(3)=a.3+b
f(3) = 3.3+(-1)
f(3)= 9 + (-1)
f(3)=8

jadi rumus f(x)=3x+(-1)