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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.