An algebra problem by Renz Mina

Algebra Level 3

Here The nested squareroot is raised infinitely many times. Solve for the value of x. Round off your answer to the nearest hundredths.


The answer is 0.59.

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1 solution

Renz Mina
Aug 1, 2016

Let u = x + x + u=\sqrt{x+\sqrt{x+\cdots}} . Then we have that u u u = 2 u^{u^{u^\cdots}}=2 . This implies that 2 ln u = ln 2 2\ln{u}=\ln{2} or that is ln u = ln 2 \ln{u}=\ln{\sqrt{2}} . We have that u = 2 u=\sqrt{2} . So 2 = x + x + \sqrt{2}=\sqrt{x+\sqrt{x+\cdots}} . This means that 2 = x + x + x + = x + 2 2=x+\sqrt{x+\sqrt{x+\cdots}}=x+\sqrt{2} . Thus x = 2 2 = 0.59 x=2-\sqrt{2}=0.59

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