fungsi f(x)=ax+b. jika f(-1)=8 dan f(3)=-12 tentukan rumus fungsi tersebut

Diketahui
f(x) = ax + b
f( -1) = 8
f( 3 ) = - 12

Penyelesaian
f (-1) = a (-1) + b
      8 = -a + b

f (3) = a (3) + b
- 12 = 3a + b

Eliminasi b
-a + b = 8
3a + b = -12
__________---
- 4a = 20
  4a = - 20
    a = - 20 ÷ 4
    a = - 5

Substitusi a = - 5
    - a + b = 8
- (-5) + b = 8
      5 + b = 8
            b = 8 - 5
            b = 3

Rumus fungsi
f (x) = ax + b
       = -5x + 3