Diketahui rumus fungsi f(x)=ax+b. Jika f(3) = 7 dan f(-5)= -25 maka rumus fungsi f(x) adalah --

f(3) = 3a+b = 7
f(-5) = -5a+b = -25  
-----> 8a = 32 <=> a = 4

3a + b = 7
3x4 + b = 7
12 + b = 7
b = -5

f(3) = 7
a.3+b = 7

f(-5) = -25
a.(-5)+b = -25

3a+b = 7
-5a+b = -25
------------------- (-)
8a =32
a=32/8= 4

3a+b = 7
3(4) + b = 7
12+b = 7
b = 7-12
b = -5

f(x) = 4x-5