Diketahui f(x) = ax + b, f(3) = 15 dan f(12) = 33. Tentukan nilai a dan b serta tentukan nilai f(7)!

f(x) = ax + b

f(3) = 15
3a + b = 15

f(12) = 33
12a + b = 33

12a + b = 33
3a + b = 15
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9a = 18
a = 18/9
a = 2

3a + b = 15
3(2) + b = 15
6 + b = 15
b = 9

maka
a = 2
b = 9

f(x) = ax + b
f(x) = 2x + 9
f(7) = 2(7)+ 9
f(7) = 14 + 9
f(7) = 23