Diketahu f(x) = ax + b jika f(2) = 1 dan f(4) = 7 maka nilai ( a-b) adalah

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

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

2a+b = 1
4a+b = 7
_______-
-2a = -6
a=-6/-2
a=3

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

Nilai a-b
= 3-(-5)
= 8