2016 is absolutely awesome 10

Algebra Level 4

1 + 2016 1 + 2017 1 + 2018 1 + 2019 1 + = ? \sqrt{1+2016\sqrt{1+2017\sqrt{1+2018\sqrt{1+2019\sqrt{1+\cdots}}}}} = \, ?


This is a part of the Set .


The answer is 2017.

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4 solutions

Let's start by forming a nested radical expession for x |x| : x = x 2 x = 1 + ( x 1 ) 1 + x ( x + 2 ) x = 1 + ( x 1 ) 1 + x 1 + ( x + 1 ) ( x + 3 ) x = 1 + ( x 1 ) 1 + x 1 + ( x + 1 ) 1 + ( x + 2 ) |x| = \sqrt{x^2}\\ |x| = \sqrt{1+(x-1)\sqrt{1+x(x+2)}}\\ |x| = \sqrt{1+(x-1)\sqrt{1+x\sqrt{1+(x+1)(x+3)}}}\\ \vdots \\ |x| = \sqrt{1+(x-1)\sqrt{1+x\sqrt{1+(x+1)\sqrt{1+(x+2)\sqrt{\cdots}}}}} Simply putting x = 2017 x=2017 gives us: 2017 = 1 + 2016 1 + 2017 1 + 2018 1 + 2019 \boxed{2017=\sqrt{1+2016\sqrt{1+2017\sqrt{1+2018\sqrt{1+2019\sqrt{\cdots}}}}}}

Moderator note:

Simple standard approach.

Amazing @Abdur Rehman Zahid

Anirban Mandal - 5 years, 5 months ago

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Thank you!!!

Abdur Rehman Zahid - 5 years, 5 months ago
Chew-Seong Cheong
Dec 24, 2015

Ramanujan's nested radical formula (equation 21) is as follows:

x + n + a = a x + ( n + a ) 2 + x a ( x + n ) + ( n + a ) 2 + ( x + n ) a ( x + 2 n ) + ( n + a ) 2 + ( x + 2 n ) . . . \small x+n+a = \sqrt{ax+(n+a)^2+x\sqrt{a(x+n)+(n+a)^2+(x+n)\sqrt{a(x+2n)+(n+a)^2+(x+2n)\sqrt{...}}}}

Substitute x = 2016 x = 2016 , n = 1 n=1 and a = 0 a=0 , we have:

2016 + 1 + 0 = 1 + 2016 1 + 2017 1 + 2018 1 + 2019 1 + . . . 2016+1+0 = \sqrt{1+2016\sqrt{1+2017\sqrt{1+2018\sqrt{1+2019\sqrt{1+...}}}}}

Therefore, S = 2017 S = \boxed{2017}

First Last
Dec 22, 2015

Ramanujan told us that: 3 = 1 + 2 1 + 3 . . . \sqrt{1+2\sqrt{1+3\sqrt{...}}} . Through manipulation, it is easy to see that: y = 1 + x 1 + ( x + 1 ) . . . y = \sqrt{1+x\sqrt{1+(x+1)\sqrt{...}}} , where y = x + 1 y = x + 1 . So then x = 1 + 2016 1 + 2017 . . . x = \sqrt{1+2016\sqrt{1+2017\sqrt{...}}} x = 2017 x = \boxed{2017}

Pulkit Gupta
Dec 22, 2015

More of a hint than solution, refer Ramanujan's infinite nested radicals.

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