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Prove that

Posted July 6th, 2009 by alpha
in

Prove that:
$ sin\frac{5\pi}{18}-cos\frac{4\pi}{9}=\sqrt{3}.sin\frac{\pi}{9} $

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Comments

hint

On July 6th, 2009 Structure says:
$$\sin\frac{5\pi}{18}=\cos(\frac{\pi}{2}-\frac{5\pi}{18})=\cos\frac{4\pi}{18}=\cos\frac{2\pi}{9}$$
$$\cos x-\cos y=-2\sin\frac{x-y}{2}\sin\frac{x+y}{2}$$

~~THANK YOU ~~

On July 8th, 2009 alpha says:

-------------------x----------------------------
``Old theorems never die; they turn into definitions.''
----E. Hewitt

''ALPHA" =)

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