Totally Radical

Algebra Level 1

5 5 5 \sqrt{5 \sqrt{5 \sqrt{5 \sqrt{\ldots } } } }

Given this string of radicals, what is its equivalent value in integers?

Hint: The given can be considered equal to "x".


The answer is 5.

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3 solutions

Prasun Biswas
Mar 13, 2014

Given problem is : 5 5 5 . . . . . \sqrt{5\sqrt{5\sqrt{5\sqrt{.....}}}}

Let this be considered as x x . So ------>

5 5 5 . . . . . = x \sqrt{5\sqrt{5\sqrt{5\sqrt{.....}}}}=x

On squaring both sides -----

5 × 5 5 5 . . . . . = x 2 \implies 5\times \sqrt{5\sqrt{5\sqrt{5\sqrt{.....}}}}=x^2

5 x = x 2 \implies 5x=x^2 [substituting original equation here]

x 2 5 x = 0 \implies x^2-5x=0

x ( x 5 ) = 0 \implies x(x-5)=0

x = 0 or x 5 = 0 x = 5 \implies x=\boxed{0} \text{ or } x-5=0 \implies x=\boxed{5}

Now, we can clearly see that x x should be more than 0 0 , i.e., x > 0 x\gt 0 .

So, the required possible value of x = 5 x=\boxed{5}

How type your solutions in that font? Nice solution by the way, very easy to read, to follow and understand :-)

Pethree Asiain - 7 years, 2 months ago

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Use LaTeX to write the math parts in such font. See the formatting guide for more details regarding the syntax for the math symbols and remember to put all the math parts within \ ( \backslash( and \ ) \backslash) like this ----->

\ ( . . . . . . . \ ) \backslash(.......\backslash)

Prasun Biswas - 7 years, 2 months ago

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Okay thanks!

Pethree Asiain - 7 years, 2 months ago
Rakesh Senwar
Mar 14, 2014

x=string ----------------(1) x^2=5string from (1) x^2=5x x=5

Edmund Sia Ii
Mar 10, 2014

Let's call the given the "[string]" because typing the given is extremely time consuming and it'll be more confusing if I typed it.Trust me.

  1. [string] = x
  2. 5[string] = x^2

Since "[string] = x", we can substitute the "[string]" on the left side of the equation with "x". That leaves us with:

  1. 5x = x^2
  2. (5x)/(x) = (x^2)/(x)
  3. 5 = x

The answer is 5

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