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# What do you think of this proof of trigonometric angle addition formula?

Asked by LostInParadise (28580)
May 6th, 2011

I am surely not the first to think of this, but this proof seems more intuitve and straightforward than the usual proofs I have seen using similar triangles. Angle Addition proof I give the proof for the cosine formula. The same diagram can be used for the sine formula.

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