Fungsi f dinyatakan dengan rumus f(x) = px + q. Jika f(-3) = 9 dan f(2) = -1 ,maka nilai f(-7) adalah ...

f(x) = px + q

f(-3) = -3p + q = 9
f(2) = 2p + q = -1

Eliminasi untuk mencari nilai p
 2p + q = -1
-3p + q = 9
----------------- -
5p         = -10
  p         = -2

Substitusi untuk mencari nilai q
2p + q = -1
2(-2) + q = -1
-4 + q = -1
q = -1 + 4
q = 3

Bentuk fungsi
f(x) = px + q
f(x) = -2x + 3

Cari nilai f(-7)
f(x) = -2x + 3
f(-7) = -2(-7) + 3
f(-7) = 14 + 3
f(-7) = 17

f(x) = px + q
f(-3) = p.-3 + q
9 = -3p + q ••• (1)
f(2) = p.2 + q
-1 = 2p + q ••• (2)

-3p + q = 9
2p + q = -1
---------------- -
-5p = 10
p = -2

2p + q = -1
2 (-2) + q = -1
-4 + q = -1
q = 3

Maka,
f(x) = px + q
f(-7) = -2 (-7) + 3
•••• = 17