suatu fungsi ditentukan dengan rumus f(x)=ax+b. Jika f(-2)=-1 dan f(5)=15 Tentukan: a.nilai a dan b b.f(3) sama caranya ya:)

Jawab :
Rumus : f(x) = ax + b

f(-2) = -2a + b = -1........(x5)
f(5) = 5a + b = 15.........(x2)

-10a + 5b = -5
10a + 2b = 30
---------------------- +
7b = -25
b = -25/7

5a + b = 15
5a + (-25/7) = 15
5a - 25/7 = 15
5a = 15 + 25/7
5a = 130/7
a = (130/7)/(5)
a = 26/7

Nilai a = 26/7
Nilai b = -25/7

f(3) = 3(26/7) - 25/7
f(3) = 78/7 - 25/7
f(3) = 53/7