Computational complexity of Fibonacci Sequence

Question

I understand Big-O notation, but I don\'t know how to calculate it for many functions. In particular, I\'ve been trying to figure out the computational complexity of the nai

Answer 1

You can expand it and have a visulization

     T(n) = T(n-1) + T(n-2) <
     T(n-1) + T(n-1) 

     = 2*T(n-1)   
     = 2*2*T(n-2)
     = 2*2*2*T(n-3)
     ....
     = 2^i*T(n-i)
     ...
     ==> O(2^n)