I'm just curious about the,

http://www.physicsforums.com/latex_i.../3041330-0.png

identities, is there a simple way to derive them?

I have a test in a few days and I don't like memorizing too much.

Thanks again!

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- Dec 16th 2010, 03:45 PMjeguesSum and Difference formulae (sin and cos)
I'm just curious about the,

http://www.physicsforums.com/latex_i.../3041330-0.png

identities, is there a simple way to derive them?

I have a test in a few days and I don't like memorizing too much.

Thanks again! - Dec 16th 2010, 03:48 PMProve It
No simple way to derive them I'm afraid - more time and effort than you can afford to waste in a test.

Just write them down and/or memorise them.

$\displaystyle \displaystyle \sin{(\alpha \pm \beta)} = \sin{\alpha}\cos{\beta}\pm\cos{\alpha}\sin{\beta}$

$\displaystyle \displaystyle \cos{(\alpha \pm \beta)} = \cos{\alpha}\cos{\beta}\mp \sin{\alpha}\sin{\beta}$.

If I can memorise them you can too :P