Trigonometric sum.

[man111]

Calculate value of $sin(\frac{\pi}{9})\times sin(\frac{2\pi}{9})\times sin(\frac{4\pi}{9})\timex=$

[ShMaxG]

It is a standart school problem! Just use some known formulas -- product of sines and cosines...

P.S. Why "sum"?

[nnosipov]

man111 в сообщении #393283 писал(а):

Calculate value of $sin(\frac{\pi}{9})\times sin(\frac{2\pi}{9})\times sin(\frac{4\pi}{9})\timex=$

Answer: $\sqrt{3}/8$. А вот сумма, похоже, ничем не замечательна.

[maxmatem]

man111
And that in this problem Olympiad? And which class is targeted for the task?

[man111]

Sorry for posting in wrong form, Now next time I will post in appropiate forum.

-- Wed Dec 29, 2010 17:41:51 --

Thanks for answer.