Trig identities?

Question

does anyone know the sum/difference identities of sin and cos? I have a test tonight and I don't have them memorized and don't have my book with me.

the sin2x and cos2x would help as well.

thanks a lot!

Answer 1

sin (a+b) = sin a cos b + cos a sine b

cos (a+b) = cos a cos b - sin a sin b

sin (a-b) = sin a cos b - cos a sin b

cos (a-b) = cos a cos b + sin a sin b

sin 2x = 2 sin x cos x

cos 2x = cos^2 x - sin^2 x

that's it!