f(x) =mx+n. Jika f(-1)=1,dan f(3)=9, maka hasil dari f(1) - f(4) adalah..

f(x) =mx+n
f(-1)=-1m+n=1
f(3)=3m+n=9
=-4m=-8
=m=2

-1m+n=1
-2+n =1
n =1+2
n =3

f (1) =mx+n
=2 (1) +3
=5

f (4) =mx+n
=2 (4) +3
=8+3
=11
f (1)-f (4) =5-11=-6