In: Advanced Math
For the Fibonacci sequence, prove the formula u2n+1 = un un+2 + (-1)n
The Febonacci sequence 
 is given by 
 where 
.
We have to prove the formula 
We shall prove this formula by using Strong Mathematical Induction on the set of natural numbers
for n = 1, the formula is 
Also from the febonacci sequence we have 
since 
hence the formula is true for n = 1.
suppose the formula is true for n = 1,2,3,...,k
that is 
........(2)
now take n = k+1,
from equation (1) we have  



using equation (2)

using equation (1)
again using equation (1)
as 


this is the formula 
 for n = k+1
Hence the formula 
 is true for n = k+1
Thus the formula 
 is true for n = 1 and if we assume that it is true for n =
1,2,3,...,k, then it is true for n = k+1
therefore by using Mathematical induction we conclude that the
formula 
 is true for every 
.
Hence for the Febonacci sequence  