Angle Addition Identities

This post includes proofs of two angle addition identities.

$ \sin(x+y) = \sin x \cos y + \sin y \cos x$

$ \cos(x+y) = \cos x \cos y – \sin x \sin y$

 

References

[1] https://www.khanacademy.org/math/precalculus/x9e81a4f98389efdf:trig/x9e81a4f98389efdf:angle-addition/v/proof-angle-addition-sine

[2] https://www.khanacademy.org/math/precalculus/x9e81a4f98389efdf:trig/x9e81a4f98389efdf:angle-addition/v/proof-angle-addition-cosine

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Christina Daniel

I am a research assistant in theoretical physics. This website, derive-it.com, serves to organize my ongoing learning and research as well as to provide a resource to other learners around the world.

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