fungsi F didefinisikan dengan rumus f(x) = ax + b. jika f(5) = 16 dan f(4) = 11 ,maka nilai f(-1) adalah

MAPEL = MATEMATIKA
KELAS = 8
BAB = RELASI & FUNGSI

diketahui :
- rumus fungsi f(x) = ax + b
- f(5) = 16
- f(4) = 11

ditanya = f(-1) ??

ans :

f(x) = ax + b
f(5) = 5a + b = 16.......... ( 1 )

f(x) = ax + b
f(4) = 4a + b = 11........... ( 2 )

eliminasi nilai b pada pers. ( 1 ) dan ( 2 )
5a + b = 16
4a + b = 11
__________-
a = 5

subtitusi nilai a = 5 pada pers. ( 1 )
5a + b = 16
5(5) + b = 16
b = 16 - 25
b = -9

rumus fungsi :
➡ f(x) = ax + b
➡ f(x) = 5x + (-9)
➡ f(x) = 5x - 9

f(-1) = 5x - 9
f(-1) = 5(-1) - 9
f(-1) = -5 - 9
f(-1) = -14

semoga membantu