# Prove the following beautiful identity of the square root of 7.

• Jun 15th 2008, 08:59 PM
mathwizard
Prove the following beautiful identity of the square root of 7.
Prove the identity

$\displaystyle -\sin \frac{\pi}{7} + \sin \frac{2\pi}{7} + \sin \frac{3\pi}{7} + \sin \frac{4\pi}{7}+\sin \frac{5\pi}{7} - \sin \frac{6\pi}{7} = \sqrt{7}$

P.S. If I find a question interesting, is there a way to save the thread to look at it later (ex. using "favorite" or "private watch list"). Is there such facility in this forum? I couldn't find any means of saving a question that I like... (Crying)
• Jun 15th 2008, 09:37 PM
Reckoner
Still working on the identity (nice one!), but

Quote:

Originally Posted by mathwizard
P.S. If I find a question interesting, is there a way to save the thread to look at it later (ex. using "favorite" or "private watch list"). Is there such facility in this forum? I couldn't find any means of saving a question that I like... (Crying)

At the top of the post, click "Thread Tools" and select "Subscribe to this thread." You can access your subscribed threads in your user control panel. Alternatively, you can go into your options and change your default thread subscription setting so that you will automatically be subscribed to all threads you post in.
• Jun 16th 2008, 01:06 AM
bobak