Math Help - yet another trig identity...

1. yet another trig identity...

Establish the identity:

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

2. What identities are you allowed to apply to this exercise?

Thank you!

3. Originally Posted by jpman

Establish the identity:

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

Hi jpman,

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

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

4. 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!