diketahui f(x)=a+bx. jika f(6)=-13, dan f(-2)=11, tentukan nilai f(3)

f(x) = a + bx

f(6) = a + 6b = -13 ......................(1)
f(-2) = a - 2b = 11 ......................(2)

dari (1) dan (2)
a + 6b = -13
a - 2b = 11
---------------- (-)
     8b = -24
       b = -3
subtitusikan nilai b = -3 ke pers. (1)
a + 6b = -13
a + 6(-3) = -13
a - 18 = -13
a = 18 - 13
a = 5

rumus f(x) = 5 - 3x
f(3) = 5 - 3(3)
      = 5 - 9
      = -4