Saturday, 9 May 2015

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

Some of you may have seen the video:




https://youtu.be/DLWpj34UNRk



It is a proof of the irrationality of $eπ$ 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 $eπ$ is irrational.



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



We conclude that $eπ$ is irrational.



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

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