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 Exercise [03.02] 
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Joined: 12 Mar 2008, 10:57
Posts: 69
Location: India
Post Exercise [03.02]
1.Let p=(2+(2+(2+(2+...)^{-1})^{-1})^{-1})^{-1}
Then
p=(2+p)^{-1}
\Rightarrow\ p=\frac{1}{p+2}\Rightarrow\ p^2+2p-1=0
orp=\frac{-2\pm{\sqrt{8}}}{2}=-1\pm{\sqrt{2}}
Hence p=-1+\sqrt{2}(because p by definition is positive)
Now,
1+(2+(2+(2+(2+...)^{-1})^{-1})^{-1})^{-1}=1+p=1-1+\sqrt{2}=\sqrt{2}
2.Let q=(1+(2+(1+(2+(1+...)^{-1})^{-1})^{-1})^{-1})^{-1}
Then
q=(1+(2+q)^{-1})^{-1}=\frac{q+2}{q+3}
\Rightarrow\ q^2+2q-2=0
orq=-1+\sqrt{3}(Neglecting the negative solution)
Now
5+\frac{1}{3+q}=5+\frac{1}{\sqrt{3}+2}=\frac{5\sqrt{3}+11}{\sqrt{3}+2}\frac{\sqrt{3}-2}{\sqrt{3}-2}=7-\sqrt{3}


13 May 2008, 12:57
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Joined: 03 Feb 2009, 03:09
Posts: 3
Post Re: Exercise [03.02]
Could you please explain how to get from

p=(2+(2+(2+(2+...)^{-1})^{-1})^{-1})^{-1}

to

p=(2+p)^{-1}


Thanks -


05 Feb 2009, 03:41
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Joined: 07 Jun 2008, 08:21
Posts: 182
Post Re: Exercise [03.02]
38fr17h9 wrote:
Could you please explain how to get from

p=(2+(2+(2+(2+...)^{-1})^{-1})^{-1})^{-1}\ \ \ \ (1)

to

p=(2+p)^{-1}


Thanks -

Since (1) in the above quote can be written as:
p=(2+q)}^{-1}} where q=(2+(2+(2+...)^{-1})^{-1})^{-1}
then since q is clearly the same sequence as p:
p=(2+p)^{-1}


05 Feb 2009, 08:38
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Joined: 11 Jul 2009, 20:45
Posts: 17
Post Re: Exercise [03.02]
1.Let p= (2+(2+(2+(2+----)exp-1)exp-1)exp-1,,,etc ='s 1/(2+p) is what you have to prove! Don't assume it at the start!


17 Jul 2009, 22:44
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Post Re: Exercise [03.02]
harried wrote:
1.Let p= (2+(2+(2+(2+----)exp-1)exp-1)exp-1,,,etc ='s 1/(2+p) is what you have to prove! Don't assume it at the start!

I don't understand what you are objecting to!! You are asked to show that the continued fraction is equal to \sqrt2.
Please explain your problem with the above proofs more fully.
Thanks


18 Jul 2009, 07:57
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Joined: 11 Jul 2009, 20:45
Posts: 17
Post Re: Exercise [03.02]
Vasco you are correct. If p is the inverse infinite sequence
p=(2+(2+(2+(2+....)exp-1)exp-1)exp-1)exp-1 then any place you start your count will give you the same infinite sequence p. Easiest is to start the count again on the second 2 giving p=(2+p)exp-1,, your solution.

The same can be done for 7-sqrt3 = 5+(3+(1+(2+(1+(2+...)exp-1)exp-1 etc
where now we let 2-sqrt3= p=1/(3+q) and q is the repeating series
q=(1+(2+(1+(2+(1+.....)exp-1)exp-1)exp-1)exp-1)exp-1
we can start counting at the second 1+(2+...... to get
q=(1+(2+q)exp-1)exp-1= 1/[1+1/(2+q)] = (2+q)/(3+q)
Multiply out the 3+q
3q+q**2=2+q,,,,,,,or q**2+2q-2=0 then q= -1+sqrt3r, q=-1-sqrt3 now from above
p=1/(3+q), taking q=-1+sqrt3
p=1/(2+sqrt3) multiply top and bottom by 2-sqrt 3
to get
p=2-sqrt3,,,,adding the 5 back to p gives
7-sqrt3=5+(3+(1+(2+(1.........etc

HOW DO I GET A MATH SYMBOL EDITOR! as you can see doing things with my setup quite messy.


23 Jul 2009, 22:54
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Joined: 07 Jun 2008, 08:21
Posts: 182
Post Re: Exercise [03.02]
There's a built in editor on this forum which is explained in "general->a guide to the forum".
For use on your computer at home you could use the one I do - it's free:
Texnic Center :
http://texniccenter.org/

You can produce pdf files with it and then attach them to your posts on this forum.


24 Jul 2009, 06:52
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