Question

Can someone please help me.

Answer 1

Given 
- f(n) values for n=1,2,3,4
- possible candidates for the function

Solution:
Method: Evaluate some of the values, for each function.  A function with ANY value not matching the given f(n) values will be rejected.

N=1, f(n)=4
f(1)=4-3(1-1)=4
f(1)=4+3^(1+1)=4+3^2=4+9=13 ≠ 4   [rejected]
f(1)=4(3^(n-1))=4(3^0)=4
f(1)=3(4^(n-1))=3(4^0)=3*1=3  [rejected]

N=2, f(n)=12
f(1)=4-3(2-1)=4-3(1)=1 ≠ 12   [rejected]
[rejected]
f(1)=4(3^(2-1)=4*3^1=4*3=12
[rejected]

Will need to check one more to be sure
N=3, f(n)=3
[rejected]
[rejected]
f(3)=4(3^(n-1))=4(3^(3-1))=4(3^2)=4*9=36   [Good]
[rejected]

Solution: f(n)=4(3^(n-1))