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Power to the 2 (Posted on 2004-02-20) Difficulty: 2 of 5
What is the limit to this sequence?

√(2)
√(2+√(2))
√(2+√(2+√(2)))
√(2+√(2+√(2+√(2))))...

In general, what is the sequence in terms of x if 2 is replaced with x?

See The Solution Submitted by Gamer    
Rating: 2.8750 (8 votes)

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Solution Solution | Comment 6 of 10 |
Let S=√(2+√(2+√(2+√(2))))...
Then S^2=2+(√(2+√(2+√(2+√(2))))...)
or S^2=2+S
S^2-S-2=0
(S-2)(S+1)=0
so S=2
---------
for the general "x"
S=√(x+√(x+√(x+√(x))))...
S^2=x+S
S^2-S-x=0
no easy factoring this time, so use:
(-b±(b^2-4ac)^.5)/2a
and use + rather than -
so S=(1+(1+4x)^.5)/2
in the limit, as x goes to infinity,
S approaches √x


  Posted by Larry on 2004-02-21 10:27:53
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