suatu fungsi ditentukan oleh rumus f(x)=a-bx. jika f(-1)=-5 dan f(2)=13, nilai f(-5) adalah

f (x) = a - bx
f (-1) = a - b (-1) = -5
a + b = -5
a = -5 - b

f (x) = a - bx
f (2) = a - b (2) = 13
-5-b -2b = 13
-3b = 18
b = -6

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

f (x) = a - bx
f (-5) = 1 - (-6)(-5)
= 1 - 30
= -29

MAPEL = MATEMATIKA
KELAS = 8
BAB = RELASI & FUNGSI

diketahui =
rumus fungsi ➡ f(x) = a - bx
f(-1) = -5
f(2) = 13

ditanya = nilai f(-5)??

f(x) = a - bx
f(-1) = a - b(-1) = -5
f(-1) = a + b = -5 ......(i)

f(x) = a - bx
f(2) = a - 2b = 13.....(ii)

Eliminasi nilai a pada pers. (i) dan (ii)
a + b = -5
a - 2b = 13
_________-
3b = -18
b = -18/3
b = -6

subtitusi nilai b
a + b = -5
a + (-6) = -5
a = -5 + 6
a = 1

rumus fungsi :
➡ f(x) = a - bx
➡ f(x) = 1 - (-6)x
➡ f(x) = 1 + 6x

nilai f(-5) :
➡ f(x) = 1 + 6x
➡ f(-5) = 1 + 6(-5)
➡ f(-5) = 1 + (-30)
➡ f(-5) = 1 - 30
➡ f(-5) = -29

semoga membantu