yet another trig identity...

**jpman** · May 27th 2009, 10:20 AM

these are getting me mad...

Please help me on this one:

Establish the identity:

$cos(\alpha+\beta) + cos(\alpha-\beta) = 2\cos\alpha\cos\beta$

Thanks in advance for your help!

**stapel** · May 27th 2009, 11:28 AM

What identities are you allowed to apply to this exercise?

Thank you!

**masters** · May 27th 2009, 11:50 AM

Originally Posted by jpman

these are getting me mad...

Please help me on this one:

Establish the identity:

$cos(\alpha+\beta) + cos(\alpha-\beta) = 2\cos\alpha\cos\beta$

Thanks in advance for your help!

Hi jpman,

This is pretty straight forward if you use the sum and difference formulas of cosine.

$\cos(\alpha \pm \beta)=\cos \alpha \cos\beta \mp \sin \alpha \sin \beta$

**jpman** · May 27th 2009, 11:59 AM

Originally Posted by masters

Hi jpman,

This is pretty straight forward if you use the sum and difference formulas of cosine.

$\cos(\alpha \pm \beta)=\cos \alpha \cos\beta \mp \sin \alpha \sin \beta$

Dude, you rock.

I totally missed the sum and difference formulas...

Thanks a bunch!

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