Can somebody solve this and give detailed description ?

I get stuck on this part 1/2 sin18..

http://img207.imageshack.us/img207/1634/firstz.jpg

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- December 14th 2009, 02:09 AMldx2Trigonometric identity
Can somebody solve this and give detailed description ?

I get stuck on this part 1/2 sin18..

http://img207.imageshack.us/img207/1634/firstz.jpg - December 14th 2009, 07:22 AMGrandadsin 18 degrees
Hello ldx2

Welcome to Math Help Forum!I agree: .

There are various ways of deriving . Here's one. And here's my version:

We then note that is also a root. Hence is a factor, which again we discard for the same reason; leaving us with the remaining factor:

Grandad - December 14th 2009, 07:49 AMldx2
Thanks for the quick reply and solving it. EDIT: I understood until the part where you say x=-1/2 is also a root and how you found out (2x+1) is also a factor. Could you explain that part in more detail ?

- December 15th 2009, 12:50 PMGrandad
- December 15th 2009, 01:04 PMldx2
LOL 'trial and error' ! Thank you for clearing it up. Could you please take a look at my other thread where i posted 2 trig. problems !