Saturday, 9 May 2015

irrational numbers - Proof for the irrationality of ('complex'ly?).*

Some of you may have seen the video:




https://youtu.be/DLWpj34UNRk



It is a proof of the irrationality of by Ron (14years) , presented by 'blackpenredpen' Youtuber.



The proof goes something like this:



We know that e^{iπ}=-1 ("Euler's famous identity").



e^{iπ}=i^2




So, π=\frac{2\ln{i}}{i}



We must prove that is irrational.



Let us assume, on the contrary, that is rational.



eπ=\frac{a}{b} where a and b are rational numbers.
eπ=e\frac{2\ln{i}}{i}=\frac{a}{b}
2eb\ln{i}=ai
\ln{i^{2eb}}=ai

\ln{(-1)^{eb}}=ai
(-1)^{eb}=e^{ai}
Squaring on both sides,
1^{eb}=e^{2ai}
1=e^{2ai}
e^0=e^{2ai}
When the bases are identical, the powers are equal.
0=2ai
a=0
Hence,

eπ=\frac{0}{b}
eπ=0
This is not possible and therefore gives us a contradiction.



This contradiction has arisen because of our incorrect assumption the is rational.



We conclude that is irrational.



(*) Is this proof legitimate? Or is there something dubious about it? If so, please point it out.

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