Question

Fungsi f ditentukan dengan rumus f(×)=ax+b.Bila f(2)=1 dan f(4)=7,maka nilai 2a-3b adalah

Answer 1

F(x) = ax + b
f(2) = 2a + b = 1
f(4) = 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)
2a - 3b = 2.3 - 3.(-5)
= 6 + 15
= 21

Answer 2

F(x) = ax + b
f(2) = a(2) + b = 1
1 = 2a + b
1 - 2a = b .......... (persamaan 1)
f(4) = a(4) + b = 7
7 = 4a + b ......... (persamaan 2)

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

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

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