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.
Follow Math Help Forum on Facebook and Google+
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. Similarly expand cos(A+B) and add,
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?
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
View Tag Cloud