Question

Are these identities correct
(trigonometry)
I would be learning them , so i want to verify

Answer 1

sin A + sin B = 2 sin ½ (A + B) cos ½ (A − B)

sin A − sin B = 2 sin ½ (A − B) cos ½ (A + B)
cos A + cos B = 2 cos ½ (A + B) cos ½ (A − B)
cos A − cos B = −2 sin ½ (A + B) sin ½ (A − B)

Answer 2

http://www.sosmath.com/trig/Trig5/trig5/trig5.html

Answer 3

or
http://www.purplemath.com/modules/idents.htm