The Law of Cosines - Proof

[@Curmudgeon1685]

mistake at 3:36. It should be b^2sin^2ϴ. You correct yourself later when yout factor out b^2.

[@rashmansoori]

shalom mr. stein! Your presentations are flawless. These videos > my math book

[@WillyGhillie]

when you distribute/multiply, I believe the last end of the equation is b^2Sin^2(theta) unless I am wrong, in which I may be

[@martingaens2073]

Nope, you're right. I was also a bit confused, had to check for myself.

[@user-uz2gb9ci7u]

brilliant ! I was finding some difficulties in figuring out the coordinates of the upper point ! Thanks so much :)

[@NicotheMerchant]

Very helpful. Thank you.

[@boompbeep5944]

Great video, Steve! It helped me understand much more comprehensively about the Law of Cosines. :-) Maybe one day I'll be able to figure out the proofs for myself...

[@dylanorlandocallecossio5663]

Muy buena explicación, gracias

[@bruceedward3079]

Beautiful proof, thanks man

[@FalconFetus8]

Thanks so much for this video. I have a very hard time memorizing formulas; I do much better when I can sort of re-create the formula on the spot when I need it. These proofs help me do that.

[@carolinacastroismybottembt9438]

Thanks Dr.Stein

[@steveocken]

Steve, nice presentation. What software are you using?

[@markanderson2372]

This video is very helpful. But in the Cosine Law, in the Distribute /Multiply line of the Distance Formula is (b sin⁡θ-0 )^2 missing a sin square?

[@steinmath]

Yes, there's a typo in the proof, as many commenters pointed out (thanks!). Hopefully you can see that it works out.

[@KayYesYouTuber]

Awesome proof. Thanks.

[@abetoymachine]

Shouldn't it be B^2sin^2theta when you first distribute/multiply the distance formula? Otherwise awesome vid!

[@Amo_Astra]

Does anyone know where the -2ab cosθ comes from in the distribute/multiply step? I don’t know how that could’ve been achieved by distributing and multiplying?

[@haleyboswell4095]

I love you math man

[@aalia8345]

Awesome

[@Anonymous71475]

Wow.... very smart...

[@marklvrd]

How does one know to start the proof by finding the endpoints first?

[@eipimath]

Thanks for sharing! I posted a short video on deriving the law of cosines, It should apply for all angles (acute, obtuse, reflex, negative). Hope to get your thoughts.

[@Aeizium]

Interesting!!!

[@ryanclarkjohnson]

A few commenters have pointed out, but I think it deserves repeating, that this video is NOT flawless. There is a major flaw in this proof that anyone watching closely should have seen. There was a sin function that should have been squared but wasn't. The error was simply fixed without explanation two steps later when the exponent was reinserted.