Funsi f ditentukan dengan rumus f(x)=ax +b jika f(2)=1 dan f(4) =7 maka nilai a+b adalah

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

f(4) = 4a+b


2a+b=1
4a+b=7......... kurangkan

-2a = -6
a=3



2a+b=1
2.3+b=1
6+b=1
b=1-6
b=-5

a+b = 3+-5= -2

Fungsi

f(x) = ax + b
f(2) = 2a + b = 1 ..... (i)
f(4) = 4a + b = 7 ..... (ii)

Eliminasi
2a + b = 1
4a + b = 7
________ _
–2a = –6
a = –6/–2
a = 3

Substitusikan nilai a
2a + b = 1
2(3) + b = 1
6 + b = 1
b = 1 – 6
b = –5

a + b = 3 + (–5)
a + b = –2