Diketahui fungsi f(x)=ax+b, jika f(2)=13 dan f(5)=22, maka nilai dari f(-8) adalah

f(x) = ax + b
f(2) = a.2 + b
13 = 2a + b ••• (1)
f(5) = a.5 + b
22 = 5a + b ••• (2)

2a + b = 13
5a + b = 22
----------------- -
-3a = -9
a = 3

2a + b = 13
2 (3) + b = 13
6 + b = 13
b = 7

Maka,
f(-8)
= a.-8 + b
= 3(-8) + 7
= -24 + 7
= -17