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# Quick double angle query

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1. Quick double angle query
Hi, so I am studying something on quadratic curves, the book doesn't ask me to do it but I like to know where they go from one formula to another. If I was a cat I would be dead

So just a quick confirmation really,

Can be obtained by rearranging and manipulating

Tried it but I got as far as

So I assume that

or would that be a wrong assumption?

Ignore me I just subbed some numbers in and can see it seems to work
Last edited by SubAtomic; 24-07-2012 at 19:01.
2. Re: Quick double angle query
Your assumption is correct. It's because , and so the minus signs cancel.
3. Re: Quick double angle query
(Original post by SubAtomic)

So I assume that

You know that you can multiply the numerator and denominator of a fraction by the same number and the fraction remains the same ... yes?

In this case you have multiplied by -1
4. Re: Quick double angle query
(Original post by TenOfThem)
You know that you can multiply the numerator and denominator of a fraction by the same number and the fraction remains the same ... yes?

In this case you have multiplied by -1
Yep, one thing goes in one thing escapes, hopefully am swapping for better things though. Don't know what I was thinking I like reassurance too much. Bit fried from all the A' B' C' u^2 uv v^2 sincos sin^2 cos^2 etc etc

Thank you both for clarifying
Last edited by SubAtomic; 24-07-2012 at 19:15.
5. Re: Quick double angle query
Not double angle I know but how does this work, don't get how the last line is equal to the second.

So how do I go about multiplying out this as this is where the problem lies I think

All I can think is I'd end up with

What do I do with the half theta squared? Does it become a quarter theta? And what do I do when multiplying by the half theta?

Back later, any help appreciated
Last edited by SubAtomic; 20-08-2012 at 16:10.
6. Re: Quick double angle query
(Original post by SubAtomic)
...
7. Re: Quick double angle query
(Original post by Lord of the Flies)
Just thought about what I did and didn't square the theta in the denom for some reason, I need to turn the theta into x for a while until it second nature, as in can just leave it as theta.

Thanks

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Last updated: August 20, 2012
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