# Mathematical Proofs: The Cosine Rule

How many times have your teacher given you a formula to use in class? How many times have you wondered where it came from? Here I will show you one of the most fantastic formula used in Mathematics! The Cosine Rule. A step by step guide as to how the Cosine rule was derived. Feel free to rewind as well as the video and learn how to prove the Cosine rule. Enjoy!!

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### 23 Responses to Mathematical Proofs: The Cosine Rule

1. DinoKicker says:

2. claudilicious6 says:

God Bless you﻿ old man.

3. xxbcmbiggestfanxx says:

now why can’t my teacher explain it like that??﻿ thanks, great video!

4. eMBLAQ says:

Thankyou! It was﻿ wonderfully explained and very easy to follow.

5. whatever534231 says:

absolutely brilliant, thankyou thankyou thankyou﻿

6. chimera66 says:

This is the best and most simplest way of proving the law. Excellent﻿ work!

7. chimera66 says:

Orange, lemon and ultra violet. Thank﻿ you.

8. Forry2087 says:

you﻿ are a genius mate! good work

9. meterotronic says:

my intuition thanks you﻿

10. meterotronic says:

The best proof yet…better than﻿ that “Khan dude….peace be with you

11. leoisrael223 says:

MAAAN SO COOL, THIS IS AN AWESOME﻿ PROOF!!

12. mountpeaceboy says:

you lost me why didn’t you just call﻿ b-x … y? that would be less confusing

13. allstargrimemusic says:

excellent video & well explained ﻿

14. lazer1235 says:

absolutely <3 your accent ahaha ‘pythag-oras﻿ the-orum’ and “substitute it in the equa-zion” xD

thank you so much! now i have﻿ a chance at passing my math test tomorrow!

16. SebAlva says:

4:37﻿ mindblown

17. sweentnhot0104 says:

@frostwow even though you draw h﻿ from angle c, or whatever other angles, it doesn’t matter.

18. frostwow says:

only half of a success. because drawing a unitcircle over the angle A would have proven useful.
and also exploring this case with﻿ what if we draw the line h from angle C, wouldve been interesting
but thanks anyway

19. Zelphii says:

this﻿ is the best video ever.

20. 4realsucka says:

Thank﻿ you so much!!! This video deserves 1,000,000 views haaaaa

21. warsilver99 says:

Thanks a bunch, really helped﻿ me out..

22. Youdontwantmyusernam says:

THANK YOU! maths homework Done!﻿

23. MrPlender says:

Brilliant! Short and﻿ simple. Thank you very much.