Fungsi f didefinisikan dengan rumus f(x) = px + q. Jika f (3) = -10 dan f (-2) = 0, maka nilai f(-7) adalah

f(x) = px + q
f(3) = -10
f(-2) = 0

3p + q = -10
-2p + q = 0
_________-
5p = -10
p = -10/5 = -2

-2p + q = 0
-2.(-2) + q = 0
4 + q = 0
q = 0 - 4 = -4

f(x) = px + q
f(-7) = -2.(-7) + -4
= 14 - 4
= 10

Dik:

 F(3) = -10

F(-2) = 0

Dit:  F(-7) = …?

Jawab:       

F(x) = px+q

F(3) = p3 +q

-10 = 3p+q     …(i)

F(x)=px+q

F(-2) = p(-2)+q

0= -2p+q       …(ii)

Eliminasi persamaan I dengan persamaan ii

3p+q=-10

-2p+q=0

--------------   -

3p-(-2p) +q-q=-10-0

3p+2p+ 0=-10-0

5p=-10

P=-10/5

P= -2

Masukan nllai p kepersamaan I atau ii

3p+q=10

3. (-2) + q=-10

q= -10+6

q= -4

masukan nilai p dan q ke f(-7) =p(-7) +q

f(-7) = -2 .(-7) + (-4)

f(-7) = 14 - 4

f(-7) = 10