Friday, August 9, 2019

Calculate the limit of a sequence



A sequence $c_n$ is defined by the following recursion
$c_{n+1} = c_n + c_{n-1}$ for every $n \geq 1$
and $c_0 = 1, c_1 = 2$.




-Let $a_n = \frac{c_{n+1}}{c_n}$, for every $n\geq 0$ and prove that
$a_n = 1 + \frac{1}{a_{n-1}}$ for every $n \geq 1$.



-Calculate the limit of the following sequence
$\frac{c_1}{c_0}, \frac{c_2}{c_1}, \frac{c_3}{c_2},...,\frac{c_{n+1}}{c_n}$ using the fact that this sequence is convergent






I tried close to everything to obtain the formula mentioned above but I did not succeed. What I obtained is $a_n=1 + \frac{c_{n-1}}{c_n}$ which is obviously wrong. As for calculating the limit, I don't have a clue what is meant by 'using the fact that this sequence is convergent'. Could anyone please help me out? Thank you in advance.


Answer




$C_{n+1}= C_n + C_{n-1}, A_n=\frac{C_{n+1}}{C_n}$



Substituting the first equation into the second equation you get: $A_n = 1 + \frac{C_{n-1}}{C_n}$.



From the second equation we can write: $C_{n-1} = \frac{C_n}{A_{n-1}}$.



Then we substitute this in our third equation and we get: $A_n= 1 + (\frac{C_n}{A_{n-1}})/C_n $.



is equal to $1 + \frac{1}{A_{n-1}}$.


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