Angle addition identities

Learn about the trigonometric angle addition identities, which help us discuss the trig values of sums of angles in terms of the trig values of the individual angles. For example, we can express sin(x+y) in terms of sin(x), sin(y), cos(x), and cos(y).

Trig angle addition identities

Using the cosine angle addition identity

Using the cosine double-angle identity

Using the trig angle addition identities

Proof of the sine angle addition identity

Proof of the cosine angle addition identity

Proof of the tangent angle sum and difference identities