Infinite square roots

Level pending

Find the value of the following expression?

2 + 2 + 2 + 2 + . . \sqrt{2+ \sqrt{2 + \sqrt{2 + \sqrt{2 + .. ∞ } } } }


The answer is 2.

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2 solutions

Anish Shah
Dec 15, 2013

Let y = 2 + 2 + 2 + 2... y = \sqrt{2 + \sqrt{2 + \sqrt{2 + \sqrt{2...∞ } } } }

Therefore, we can say that,

y = 2 + y y = \sqrt{2 + y }

y 2 = 2 + y y^{2} = 2 + y

y 2 y 2 = 0 y^{2} - y - 2 = 0

( y 2 ) ( y + 1 ) = 0 (y-2)(y+1) = 0

y = 2 , 1 y = \boxed{2, -1}

y can not be equal to -1 since square root can never be negative. So, (\ \boxed{y = 2} )

y = 2 *

Anish Shah - 7 years, 5 months ago

Why can't the value be infinity? If y '=' infinity, then 2 + y \sqrt{2+y} '=' infinity too.

Calvin Lin Staff - 7 years, 5 months ago

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Hi Calvin,

Here, Infinity means that the 2 + \sqrt{2 + } goes on for inifinity.

Anish Shah - 7 years, 5 months ago

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Hey...I got confused for a sec too...but I realized you probably meant that the series continues to infinity...!!!

Tanya Gupta - 7 years, 3 months ago

is the problem not clear? Sorry..

Anish Shah - 7 years, 5 months ago
Sai Aryanreddy
Nov 1, 2014

\sqrt{2+\sqrt{2+\sqrt{2\sqrt{2+\sqrt{2}+}}}}........be x then,you can write it as,\sqrt{2+x} x=\sqrt{2+x} x^{2}=2+x that implies x=2

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