di ketahui f(x) = px+q, F(1) = -5 dan f(3) = -1. nilai f(9) adalah...

1p+q=-5
3p+q=-1
______ -
-2p=-4
p=2

1p+q=-5
1(2)+q=-5
2+q=-5
q=-5-2
q=-7

f(x)=px+q
f(x)=2x+-7

ditanya f(9)
f(9)=2(9)+(-7)
=18+(-7)
=11