I believe they are about the similar in shape unless you have answers to them?
Answer:
The value of f(3) is -2.
Step-by-step explanation:
This is a recursive function. So

Now, we find f(2) in function of f(1). So


Now, with f(2), we can find the value of f(3).


The value of f(3) is -2.
Let

In order to prove this by induction, we first need to prove the base case, i.e. prove that P(1) is true:

So, the base case is ok. Now, we need to assume
and prove
.
states that

Since we're assuming
, we can substitute the sum of the first n terms with their expression:

Which terminates the proof, since we showed that

as required