Basic Trigonometric Identities (Equations)

cos (A - B)

cos A cos B + sin A sin B

cos (A + B)

cos A cos B - sin A sin B

sin (A + B)

sin A cos B + cos A sin B

sin (A - B)

sin A cos B - cos A sin B

sin 2x

2 sin x cos x

cos 2x (1)

1 - 2 sin² x

cos 2x (2)

cos² x - sin² x

cos 2x (3)

2 cos²x - 1

tan (A + B)

(tan A + tan B) / (1 - tan A tan B)

tan (A - B)

(tan A - tan B) / (1 + tan A tan B)

tan 2x

2 tan x / (1 - tan² x)

Pythagorean Identities

sin² x + cos² x = 1

1 + tan² x = sec² x,

1 + cot² x = csc² x.