Solution to Puzzle #126: The Tricky Square Root

Again received an overwhelming number of answers to this puzzle. People who answered it correctly included Pratik Poddar, Anant Aggarwal, Siddharth Mulherkar, Suman Saraf, P R Kumar and Amit Mittal. The puzzle had a simple trick to it, which is that the phrase we are trying to get to is embedded itself within the phrase.

I am reproducing the answer from Pratik Poddar.

Lets say that the value is x.
sqrt (12+x) = x
x^2 – x – 12 = 0
(x-4)(x+3) = 0
x = 4 (since x>0)

Hope you all enjoyed the puzzle!


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2 Responses to Solution to Puzzle #126: The Tricky Square Root

  1. Suman says:

    Btw, I had posted a comment on the original puzzle (not the solution) which appears to have been deleted. I am reproducing it again

    If we assumed it was a converging series we could also have replaced the expressions like
    x = sqrt(12+sqrt(12+x))
    this would yield an equation of the 4th degree
    x^4 – 24*x^2 – x + 132 = 0
    which could be factorized as
    (x-4)(x+3)(x^2 + x – 11) = 0
    the two positive roots are 4 and (3*sqrt(5) – 1)/2

    Similarly we could extend it to higher orders and find more positive roots. Wouldn’t all of them be satisfactory solutions?


    • Alok Goyal says:

      Suman, this one has stumped me, I did not think of a second order substitution. Even though the equation solves with these values, I am still having a hard time as the value is approx 2.8 which seems impossible.

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