fungsi f ditentukan dengan rumus f(x) = ax + b bila f(2) = 1 dan f(4) = 7 maka nilai 2a – 3b adalah

f(x) = ax + b
f(2) = a(2) + b = 1
            2a + b = 1

f(4) = a(4) + b = 7
          4a + b = 7

Eliminasi
2a + b = 1
4a + b = 7
--------------- -
-2a = -6
a = 3

2a + b = 1
2(3) + b = 1
6 + b = 1
b = 1 - 6
b = -5

2a - 3b = 2(3) - 3(-5) = 6 + 15 = 21