F(x)=ax-2b,jika f(5)=20 dan f(4)=12,f(8) + f(9)

Suatu fungsi dirumuskan dengan
f(x) = ax - 2b

Jika,
f(5) = a(5) - 2b = 20 (1)
f(4) = a(4) - 2b = 12 (2)

Ditanya,
f(8) + f(9) =

Jawab :
Eliminasi dahulu
f(5) = a(5) - 2b = 20
f(4) = a(4) - 2b = 12
--------------------- -
a = 8
masukkan hasil a ke persamaan (1)
f(5) = a(5) - 2b = 20
f(5) = 8(5) - 2b = 20
f(5) = 40 - 2b = 20
f(5) = -2b = -60
f(5) = b = 30

f(8) = 8(8) - 2(30)
f(8) = 64 - 60
f(8) = 4

f(9) = 8(9) - 2(30)
f(9) = 72 - 60
f(9) = 12

f(8) + f(9) =
4 + 12 = 16