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Possible Duplicate:
infinite product of sine function

Here is an other one which is more or less what Euler did in one of his proofs.

The function sinx where x∈R is zero exactly at x=nπ for each integer n. If we factorized it as an infinite product we get

How to prove $$ \sin x=...(1+\frac{x}{3\pi})(1+\frac{x}{2\pi})(1+\frac{x}{\pi})x(1-\frac{x}{3\pi})(1-\frac{x}{2\pi})(1-\frac{x}{\pi})... $$

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marked as duplicate by userNaN, Argon, Martin Sleziak, Chris Eagle, J. M. Oct 18 '12 at 8:06

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Courtesy of Edmund Landau, from his Differential and Integral Calculus.

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I don't have that book, and which part of a usual book on Mathematical Analysis could I find the proof in,like Zorich's 《Mathematical Analysis》 or ГригорийМихайлович Фихтенгольц‘s 《Calculus course》. I mean what topic it is included in? –  Miao Oct 17 '12 at 23:36
    
I need theorem 233 –  Lucas Zanella Sep 18 '13 at 4:01
    
@LucasZanella You can google the book, it is called "Differential and Integral Calculus" by Edmund Landau. –  Pedro Tamaroff Sep 18 '13 at 4:19

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