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**Honore****Member**- Registered: 2005-12-14
- Posts: 1

Hello,

Since I could not solve the following equation though applying all information I have about trigonometry, I would very appreciate if anybody could help or make some suggestion. Thanks for your time.

cos(2pi/11)+cos(4pi/11)+cos(6pi/11)+cos(8pi/11)+cos(10pi/11)=?

(Answer: -1/2)

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**ryos****Member**- Registered: 2005-08-04
- Posts: 394

Those angles be not on the unit circle, matey. Aaargh!

Ahem. I don't think they have coterminal angles on the unit circle, either.

Which means...use a calculator! Right? Don't tell me there's a goofy trig identity that will come to the rescue. I hates trig identities.

El que pega primero pega dos veces.

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

I didn't know it be talk like a pirate day. Yarr!

That scurvy dog, ryos, be correct. There be no identity that will rescue ye, landlubber.

At least, none that me or my parrot know. Arr!

Why did the vector cross the road?

It wanted to be normal.

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**Chaotic Neutral****Member**- Registered: 2005-10-31
- Posts: 55

Aye aye, captain Rottingham! Calculators at deck, rrreform in rradials if ye think it will make ye life easier.

As at night, we realise we will never Know and further thinking is pointless....Yet we start again and again

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,552

Me only contribution, mateys, is this ere lubberly sketch-ning

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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