thb96
§
$$\sin x = 2\sin \frac{x}{2}\cos \frac{x}{2} = 4\sin \frac{x}{4}\cos \frac{x}{4}\cos \frac{x}{2} = ... = {2^n}\sin \frac{x}{{{2^n}}}\prod\limits_{k = 1}^n {\cos \frac{x}{{{2^n}}}} $$
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