Cosine Rule Proof

@MathsTulla. Cosine Rule Proof. Derivation Cosine Rule. Law of Cosines. Leaving Cert Higher Level Math. Trigonometry.

[@tanelkagan]

I've seen the alternative proof involving the dropping of an altitude, which is then expressed in two equivalent forms based on the other sides/angles and then eliminated, but for some reason this proof is more satisfying...

[@tullamaths]

Yes, where they make it two right angled triangles and use Trigonometric ratios. I prefer this method too !!

[@eipimath]

I really like this proof! I made a similar video on the law of cosines, hope to get your thoughts.