prove that

I have tried for quite a while, but am completely stuck now.

Can anyone have ago?

Thanks.

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- Jan 12th 2010, 01:30 PMTweetyprov trig indentity
prove that

I have tried for quite a while, but am completely stuck now.

Can anyone have ago?

Thanks. - Jan 12th 2010, 01:50 PMpickslides
- Jan 12th 2010, 01:59 PMArchie Meade
Hi Tweety,

first factorise..

I guess you have a typo,

i reckon your original expression should have +1 instead of -1. - Jan 12th 2010, 02:11 PMTweety
- Jan 12th 2010, 02:17 PMArchie Meade

- Jan 12th 2010, 02:25 PMpickslides
- Jan 12th 2010, 02:57 PMTweety
- Jan 12th 2010, 03:21 PMArchie Meade
The method that pickslides used was very neat, Tweety.

He used the same identity at each step.

You may see the identity written as

Rearranging this, we get

so

He simply used this, by letting A=2x to get cos4x

and the powers of x follow.

I started with the powers and worked back, eventually using that identity,

but i also used

in writing

The other identity i used is