Help understanding Recursive algorithm question We have a function that is defined recursively by $f(0)=f_0$, $f(1)=f_1$ and $f(n+2) = f(n)+f(n+1)$ for $n\geq0$

For $n\geq0$, let $c(n)$ be the total number of additions for calculating
  $f(n)$ using $f_0$ and $f_1 $ as input with $c(0) = 0$ and $c(1) = 0$. For $n \geq 2$,
  express $c(n)$ using $c(n-1) $ and $c(n-2)$
Determine if $c(n)\geq2^{(n-2)/2}$ for $n\geq2$ and prove your answer.

I'm lost as to what to do with this question.

In reality, only n-1 additions are needed. The only formula that we can use is f(n+2) = f (n+1) + f (n) for n >= 0. If f0 and f1 are given, the only value this formula allows us to calculate is 
f2 = f1 + f0 (applying the formula with n = 0)

Now with f2 available as well, the only value the formula allows us to calculate is
f3 = f2 + f1 (applying the formula with n = 1)

and so on. 
I'd express the number of additions as
c(n) = c(n−1) + 1

or if you insist on using c(n-2) in the formula then 
c(n) = c(n−1) + 1 + 0 * c(n-2)

