1. ## Compound Angle Formula.

I just started learning Trig identities and i've never been so confused in my life! Can someone please explain how to do this?

Prove: cos (A-B) - cos (A+B) = 2sin (A) sin (B)

Thanks.

2. Originally Posted by Tina7906
I just started learning Trig identities and i've never been so confused in my life! Can someone please explain how to do this?

Prove: cos (A-B) - cos (A+B) = 2sin (A) sin (B)

Thanks.
Hi, Tina, welcome to MHF,
According to the compound angle formula expand
cos(A-B) = cosA*cosB +sinA*sinB.

3. Thank you!

I did that at first and that's where i got stuck.
Im not actually sure how to add and make it equal 2sin (A) sin (B).

Would you be able to explain further?

4. Originally Posted by Tina7906
Thank you!

I did that at first and that's where i got stuck.
Im not actually sure how to add and make it equal 2sin (A) sin (B).

Would you be able to explain further?
cos(A+B) = cosA*cosB -sinA*sinB
cos(A-B) = cosA*cosB + sinA*sinB
So
cos(A-B) - cos(A+B) = 2sinA*sinB