suatu fungsi f(x)=px+q doketahui f(1)=5 dan f(3)=-1.nilai f(-1) adalah..

f(x) = px + q

f(1) = 5
p(1) + q = 5
p + q = 5
p = 5 - q

f(3) = -1
p(3)+ q = -1
3p + q = -1

Substitusikan
3p + q = -1
3(5 - q) + q = -1
15 - 3q + q = -1
-2q = -1 - 15
-2q = -16
q = 8

p = 5 - q
p = 5 - 8
p = -3

bentuk fungsi
f(x) = -3x + 8

f(-1) = -3(-1) + 8
= 3 + 8
= 11