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**seiya_001****Member**- Registered: 2005-08-23
- Posts: 19

can anybody tell me how to change

1 phi

- ( ∫ A sin x . cos nx dx)

phi 0

into:

A 1 phi

- . - . ∫(sin (1+n)x + sin (1-n)x )dx

phi 2 0

thanks before...

**"If you can't have more age in your life, then have more life in your age..**

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Is your question:

To:

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**seiya_001****Member**- Registered: 2005-08-23
- Posts: 19

phi as in 180 deg... or is it pi

**"If you can't have more age in your life, then have more life in your age..**

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

That's pi. Phi is normally the "vertical" (not sure exactly what to call it) angle when you are in spherical coordinates.

To:

First step, as always, is to simplify:

Now it becomes fairly simple, just use the trig identity:

Where a = x and b = nx

Which simplifies to:

*Last edited by Ricky (2006-01-11 14:08:55)*

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**seiya_001****Member**- Registered: 2005-08-23
- Posts: 19

thanks a lot bro

btw, do you have any reference where i can get a sumary of trig identity? thanks again...

**"If you can't have more age in your life, then have more life in your age..**

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

I have put it on my list to either create or find a website with even the most obscure trig identities. So far, wikipedia (as always) is the best:

http://en.wikipedia.org/wiki/Trig_identities

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**seiya_001****Member**- Registered: 2005-08-23
- Posts: 19

thank you for the information...

god bless..

**"If you can't have more age in your life, then have more life in your age..**

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