Square Root Scramble

Algebra Level 1

Find the value of x x if x + x + x + = 6 \sqrt{x + \sqrt{x + \sqrt{x + \dotsb}}} = 6 .

6^(1/2) 20 30 6^(1/100)

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5 solutions

Chew-Seong Cheong
Jul 15, 2018

x + x + x + = 6 Squaring both sides x + x + x + x + = 36 Note that x + x + x + = 6 x + 6 = 36 x = 30 \begin{aligned} \sqrt{x+ \sqrt{x+ \sqrt{x+\cdots }}} & = 6 & \small \color{#3D99F6} \text{Squaring both sides} \\ x + \color{#3D99F6}\sqrt{x+ \sqrt{x+ \sqrt{x+\cdots }}} & = 36 & \small \blue{\text{Note that }\sqrt{x+ \sqrt{x+ \sqrt{x+\cdots }}} = 6} \\ x + \color{#3D99F6}6 & = 36 \\ \implies x & = \boxed{30}\end{aligned}

I do not get it

Lyndon Lua - 2 months, 3 weeks ago

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I have added a note to explain. Hope it helps.

Chew-Seong Cheong - 2 months, 3 weeks ago
Ram Mohith
Jul 14, 2018

Given : x + x + x + = 6 \sqrt{x + \sqrt{x + \sqrt{x + \dotsb}}} = 6

Now if we take one from infinity the result is still infinity .

x + 6 = 6 \implies \sqrt{x + 6} = 6

x + 6 = 36 \implies x + 6 = 36

x = 30 \implies x = 30

Aaryan Vaishya
Dec 9, 2018

Another way to solve it would be to take the equation and notice that the equation contains itself.So we get sqrtx+6=6,then x+6=36,and finally x=30.

Gabor Koranyi
Aug 16, 2018

Same as Cheongs.

Arjun Shrivastava
Jul 13, 2018

Let \[ x + x + x + . \[\sqrt{x + \sqrt{x + \sqrt{x + \dotsb}}}. \) *be called the "mess" which is equal to 6. If we square the equation the we get x + the"mess" = 36 because the square roots are infinite so x = 36 - "mess" = 36 - 6 = 30 *

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