Continued fraction

find x such that

1+11+11+ =x
.
.
1+1x

8 Answers

11
Shaswata Roy ·

It is not that difficult
Ok here is the solution:

If we start solving the continued fraction from below we will find that-

1+1x=x+1x

1+1x+1x=1+xx+1=2x+1x+1

1+12x+1x+1=1+x+12x+1=3x+22x+1

After solving a few more of those we will find the other freactions are 5x+33x+2,8x+55x+3 and hence the
fibonnaci series is becoming visible as each of the fractions are of the form :

fn+1x + fnfnx + fn-1 where fn is the nth term of the fibonacci series

This is because:

1+1fn+1x + fnfnx + fn-1 =fn+2x + fn+1fn+1x + fn

thus we find that

fn+1x + fnfnx + fn-1 =x

on solving which we find the quadratic equation:

x2-x-1=0 hence x =1+/-√52

Another way of solving is if we assume that x+1x=x

The LHS does converge because:

fn+1x + fnfnx + fn-1 =2fnx + fn-1fnx + fn-1 =fnxfnx + fn-1 +1

Since fnxfnx + fn-1 converges the LHS converges

1
sri 3 ·

This simplifies to 11+x = x . Do u know the answer ? Is there no real solution to this question ??

30
Ashish Kothari ·

I guess its rather 1+\frac{1}{1+x}=x , which gives x^2=2 .

1
sri 3 ·

Sorry got confused with the question. I thought it was 11+11+ .... . And yeah #3 is correct.

341
Hari Shankar ·

you know, before you do that neat trick, you have the responsibility to prove that that expression on LHS actually converges.

30
Ashish Kothari ·

Sir I never gave much thought seeing it under the IX-X section.
@ Prophet Sir - I have a very vague idea abt convergence. Can you please tell me where I can read about it, somewhat easy explanation?

11
Shaswata Roy ·

@Sri & @Ashish the question simplifies to 1+1x=x

This was the easy proof...can you give me another proof.(hint: start solving the continued fraction and you will find a form of a fibonnaci series)

1
sri 3 ·

@ hsbhatt Sir : I dont know much (well almost anything) about that. Iam still in 11th. Even calculus is a bit much for me :P
@ Shaswata : Sorry. I need to know a lot more to give a proof using fibonacci series :\ :(

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