Number_Th_problem

Algebra Level 4

Let x = ( 2 + 3 ) 2012 x = (2+\sqrt3)^{2012} . Let f f denote the fractional part of x x . Find x ( 1 f ) x(1-f) .

1 1 0 0 2 2 2 + 3 2+\sqrt3

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1 solution

James Wilson
Jan 7, 2021

Perhaps this will help someone interested in seeing a solution: this link leads to math.stackexchange.com

Since ( 2 + 3 ) 2012 + ( 2 3 ) 2012 (2+\sqrt{3})^{2012}+(2-\sqrt{3})^{2012} is an integer (which is shown via an application of the binomial theorem at the provided link) and 2 3 < 1 2-\sqrt{3}<1 , we have f = 1 ( 2 3 ) 2012 f=1-(2-\sqrt{3})^{2012} .

Therefore, x ( 1 f ) = ( 2 + 3 ) 2012 ( 1 ( 1 ( 2 3 ) 2012 ) ) = ( 2 + 3 ) 2012 ( 2 3 ) 2012 = ( 4 3 ) 2012 = 1 x(1-f)=(2+\sqrt{3})^{2012}(1-(1-(2-\sqrt{3})^{2012}))=(2+\sqrt{3})^{2012}(2-\sqrt{3})^{2012}=(4-3)^{2012}=1

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