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Algebra Level 2

1 + 2014 1 + 2015 1 + 2016 1 + 2017 × 2019 = ? \large{\sqrt{1+2014\sqrt{1+2015\sqrt{1+2016\sqrt{1+2017\times 2019}}}}} = \ ?


The answer is 2015.

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2 solutions

We note that: 1 + ( n 1 ) ( n + 1 ) = 1 + n 2 1 = n 2 = n \sqrt{1+(n-1)(n+1)} = \sqrt{1 + n^2 - 1} = \sqrt{n^2} = n .

Therefore, we have:

1 + 2014 1 + 2015 1 + 2016 1 + 2017 × 2019 = 1 + 2014 1 + 2015 1 + 2016 × 2018 = 1 + 2014 1 + 2015 × 2017 = 1 + 2014 × 2016 = 2015 \sqrt{1+2014\sqrt{1+2015\sqrt{1+2016\sqrt{1+2017\times 2019}}}} \\ = \sqrt{1+2014\sqrt{1+2015\sqrt{1+2016\times 2018}}} \\ = \sqrt{1+2014\sqrt{1+2015\times 2017}} \\ = \sqrt{1+2014\times 2016} \\ = \boxed{2015}

@Tanishq Varshney Nice problem.

Abhishek Sharma - 6 years ago

( x + n ) 2 = x 2 + 2 x n + n 2 = x 2 + n ( x + ( x + n ) ) \begin{aligned} (x+n)^{2} = x^{2} + 2xn + n^{2} \\= x^{2} + n(x + (x+n)) \end{aligned}

We can continue with this method , but it'll have a limited scope , so to cover a whole new level of possible expressions , let's introduce a new variable k into the expression .

x + n = x 2 + n ( x k + ( x + ( n + k ) ) ) = x 2 + n ( x k + x 2 + ( n + k ) ( x k + x 2 + ( n + 2 k ) ( x k + x+n = \sqrt{ x^{2} + n(x - k + (x + (n+k)))} \\= \sqrt{x^{2} + n(x-k + \sqrt{x^{2} + (n+k)\cdot (x-k + \sqrt{x^{2} + (n+2k)\cdot (x- k + \dots }}}

Now , we just have to set the values of n=2014 and x=1 .

Hence , the L.H.S becomes 1+2014 = 2015 .

Earlier I used to be terrified and used to hate solving such questions(no offense Tanishq!) but ever since I learnt this method , I have been in a position to solve almost all questions of this type ;)

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