Jawaban:

Penyelesaian :

Diketahui f(x) = ax + b, jika f(2) = 5 dan f(-1) = -4. Maka tentukan f(1) + f(4)!

• f(x) = ax + b
• f(2) = 5
• f(-1) = -4

Buat persamaan dari rumus f(x)

f(x) = ax + b

f(2) = a(2) + b = 5

2a + b = 5 ... (i)

f(-1) = a(-1) + b = -4

-a + b = -4 ... (ii)

Eliminasi b dari persamaan

2a + b = 5

-a + b = -4 -

3a = 9

a = 9/3

a = 3

Substitusi nilai a ke pers (ii)

-a + b = -4

-(3) + b = -4

-3 + b = -4

b = -4 + 3

b = -1

Maka nilai dari f(1) + f(4)

f(x) = ax + b

f(1) = 3(1) + (-1)

= 3 + (-1)

= 2

f(x) = ax + b

f(4) = 3(4) + (-1)

= 12 + (-1)

= 11

Nilai f(1) + f(4)

f(1) + f(4) = (2) + (11)

= 2 + 11

= 13