Thread: yet another trig identity...

these are getting me mad...

Please help me on this one:

Establish the identity:

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

Thanks in advance for your help!

What identities are you allowed to apply to this exercise?

Thank you!

Originally Posted by jpman

these are getting me mad...

Please help me on this one:

Establish the identity:

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

Thanks in advance for your help!

Hi jpman,

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

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

Originally Posted by masters

Hi jpman,

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

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

Dude, you rock.

I totally missed the sum and difference formulas...

Thanks a bunch!