Diketahui fungsi rumus f(x) = ax + b. Jika f(2)= 13 dan f(15)=22, maka nilai f(-2) adalah

Bab Fungsi
Matematika SMP Kelas IX

f(x) = ax + b

f(2) = 2a + b = 13
f(15) = 15a + b = 22
---------------------------- -
-13a = -9
a = 9/13

2a + b = 13
b = 13 - 2 . 9/13
b = 151/13

f(x) = 9x/13 + 151/13
f(-2) = 9 . (-2) / 13 + 151/13
f(-2) = 133/13 = 10 3/13