SOLUTION: Solve For Y: {sqrt{y+sqrt{y+sqrt{y+..}}}=5}

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Question 1149213: Solve For Y: {sqrt{y+sqrt{y+sqrt{y+..}}}=5}
Answer by ikleyn(52784) About Me  (Show Source):
You can put this solution on YOUR website!
.

You are given


    sqrt%28y+%2B+sqrt%28y+%2B+sqrt%28y+%2B+sqrt%28y+%2B+ellipsis%29%29%29%29 = 5.          (1)


Square both sides.  Then the very first square root sign goes away, and you get


    y + sqrt%28y+%2B+sqrt%28y+%2B+sqrt%28y+%2B+sqrt%28y+%2B+ellipsis%29%29%29%29  = 25.    (2)


In the left side, the second addend is equal to 5, again (!)


So, your equation  (2)  takes the form


    y + 5 = 25.     (3).


From (3), you momentarily get


    y = 25 - 5 = 20.


ANSWER.  y = 20.

--------------

    It is not a joke.  It is the standard way to solve such problems.


    CHECK.  Consider this sequence

            sqrt%2820%29 = 4.472...

            sqrt%2820%2Bsqrt%2820%29%29 = 4.947...

            sqrt%2820+%2B+sqrt%2820+%2B+sqrt%2820%29%29%29 = 4.995...


You see the sequence, which, OBVIOUSLY, converges, and converges to the value of 5.


/\/\/\/\/\/\/\/

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    - Evaluating expressions that contain infinitely many square roots
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