Log the log

Algebra Level 3

Given that 2 x = x 2 65520 \large 2^{x} = x^{2^{65520}} , find the value of log 2 ( log 2 x ) \log_{2}({\log_{2}{x}}) .


The answer is 16.

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1 solution

Jeremy Galvagni
Apr 8, 2018

Taking the base-2 logarithm of both sides of the original equation gives

x = 2 65520 log 2 x x = 2^{65520}\log_{2}x

doing so again gives

log 2 x = 65520 + log 2 ( log 2 x ) \log_{2}x = 65520 + \log_{2}(\log_{2}x)

Note that 2 16 = 65536 = 65520 + 16 2^{16}=65536 = 65520+16

And letting log 2 ( log 2 x ) = 16 \log_{2}(\log_{2}x)=16 so that log 2 x = 65536 \log_{2}x=65536 we get a perfect solution so indeed

log 2 ( log 2 x ) = 16 \boxed{\log_{2}(\log_{2}x)=16}

Judging from your solution I gather you meant the equation in the question to be

2 x = x 2 65520 \Large 2^{x} = x^{2^{65520}} .

Brian Charlesworth - 3 years, 2 months ago

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thanks. still getting the hang of latex

Jeremy Galvagni - 3 years, 2 months ago

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