sin(A-B)=sin(A)cos(B)-cos(A)sin(B) proof - geometrical

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  • Опубліковано 1 січ 2025

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  • @deepaksharma790
    @deepaksharma790 4 роки тому +3

    Thankusooomuch....such a fruitful channel 🥰

  • @rajatrajat4252
    @rajatrajat4252 5 років тому +4

    Great explanation , AWESOME

  • @श्यामा-ग1न
    @श्यामा-ग1न 6 років тому +3

    Very simple explanation ....tq ..Sir

  • @pikharg
    @pikharg Рік тому +1

    Very good. It helps me to find a proof of Euler's formula without using power series and accessible from A level (I needed it to prove the derivative of sin x )

  • @roc7582
    @roc7582 7 років тому +5

    No question here, as the proof is crystal clear. I just wanted to say thank you for sharing!

  • @jippyjlock477
    @jippyjlock477 2 роки тому +1

    I understand how to derive the formula from the shape, but how do I derive the shape itself? Where does it come from? Thanks for the video!

    • @mathematics.proofs
      @mathematics.proofs  2 роки тому

      You can find most of my drawings on instagram.com/mathematics.proofs but since this video is very old, it will be right near the bottom. Hope that helps!

  • @Baabaa-ed1nf
    @Baabaa-ed1nf 5 років тому +2

    YOUR PROOF IS GOOD BUT HOW DID YOU DRAW THIS DIAGRAM

    • @mathematics.proofs
      @mathematics.proofs  5 років тому

      I can't remember to be honest. Was a very long time ago.

  • @abhradeepdey9054
    @abhradeepdey9054 4 роки тому +2

    There goes a thumbs-up from me!! Keep doing the good work:)

  • @narusaha2890
    @narusaha2890 7 років тому +5

    Nice explanation but how os=1,as you've said in this video.

    • @mathematics.proofs
      @mathematics.proofs  7 років тому

      You shouldn't be asking how it is... As you can see, it just is. When OS=1, the proof comes out. If you want to play with the value of OS, you're more than welcome to. The chances are, the same proof will come out, so it's a pointless exercise. Don't take my word for it though... Get a pen and paper and play with its value. You don't need my help to do it.

    • @mathematics.proofs
      @mathematics.proofs  7 років тому +2

      Your question is a common question, but the least important. When OS=1, the proof comes out. It's all that matters. I'm sure that if you change its value to 2.7189 you'll still get the same proof. If you want your question answered, perform experiments. Don't wait for teachers or so called 'experts' to do your thinking for you. Great maths students play around with proofs and aren't afraid to make mistakes.

    • @greatinmails5636
      @greatinmails5636 7 років тому +2

      bro that is somewhat rude and discouraging u sholld have written that in order to get the proof easily this assumptoon has been made

    • @mathematics.proofs
      @mathematics.proofs  7 років тому

      I'm someone who's pretty direct. Some people like it, some don't. I won't be making assumptions as to how @Naru Saha reacted to my comments. Since I support free speech, you are entitled to voice your opinions without being censored. This is a channel for everyone and they can respond in whatever manner they'd like to. We're here to talk and share ideas. What you regard as rude may simply be a matter of perspective. ;-)

    • @mathematics.proofs
      @mathematics.proofs  7 років тому

      Enjoy the channel, enjoy the moment and enjoy the maths. I spend my valuable time and energy giving back to people. I don't distort the facts or sugar coat my comments. I have confidence in my followers. They are capable and intelligent. They're here to get something they won't get in classrooms.

  • @madhusinghalike584
    @madhusinghalike584 6 років тому +1

    Can't we keep d os as os other than 1

    • @mathematics.proofs
      @mathematics.proofs  6 років тому

      Doesn't matter what you turn it into mate, you get the same formula at the end of your trials and tribulations. Call it 'k' if you like.

  • @balyoz3349
    @balyoz3349 3 роки тому +1

    Thank you very much

  • @Tanmoy_dey_genshin
    @Tanmoy_dey_genshin 7 років тому +1

    Can you make another video to explain why it taken as 1

    • @Tanmoy_dey_genshin
      @Tanmoy_dey_genshin 7 років тому +1

      I would be very helpful if u do that

    • @mathematics.proofs
      @mathematics.proofs  7 років тому

      Lol. I get this question so often. It just is 1, that's all. Make it whatever you want it to be... You'll end up with the same result. There's nothing special about it being 1. Even if it was pi, you'd still get the same proof. Mathematicians used 1 out of convenience. It really is a pointless question. :-D

    • @mathematics.proofs
      @mathematics.proofs  7 років тому +2

      I won't be making a video about it, as there is no need to. I'd have nothing to say. You're complicating beyond necessity. In maths and likewise in nature, sometimes you have to accept that things are just the way they are. Sometimes there are no reasons. You do something random and you end up making a discovery. This is one of those things. Take this as an example... We know that gravity exists - but we don't really know why it exists. It's just here and we experiment with it. By experimenting with it, we learn more about it, which enables us to develop technologies such as satellites that orbit around planet Earth.
      Your question leads to a philosophical dead end. It leads to questions as to why mathematics even exists.

    • @mathematics.proofs
      @mathematics.proofs  7 років тому +1

      I'll end by saying... Your question is like asking why did sin(A-B)=sin(A)cos(B)-cos(A)sin(B) pop out? Why didn't any other proof pop out? What can I say? Someone, somewhere just experimented with the diagram in the video, and out popped the proof sin(A-B)=sin(A)cos(B)-cos(A)sin(B). It's as simple as that. :-D

    • @Tanmoy_dey_genshin
      @Tanmoy_dey_genshin 7 років тому +2

      okkkk thaxxx for your help see yaa at next video

  • @lohagash
    @lohagash 6 років тому +3

    Easy explanation

  • @sukhpreetsinghgill6814
    @sukhpreetsinghgill6814 6 років тому +3

    Very good exaplations☺☺☺☺☺

  • @stevenhutton2691
    @stevenhutton2691 6 років тому

    I see you have removed 'Amazing' video from the title of your proof. Well done! You have recognized something at least. For those who might be interested see comments below.

  • @fatinishrakarian2267
    @fatinishrakarian2267 5 років тому +1

    thanks

  • @mkingasana400
    @mkingasana400 4 роки тому +2

    Nice

  • @BinodKUMAR-km3ly
    @BinodKUMAR-km3ly 8 років тому +2

    good

  • @ccottage
    @ccottage 8 років тому

    This seems a little over-complicated. You can tell that the angle you derive as 90-A in step 3 simply by saying this is an right-angled triangle, and the angle at the bottom left is A.

    • @TH-mx5ek
      @TH-mx5ek 8 років тому +2

      Ian Sergeant There's nothing complicated about it. It's a short video with a few instructions. Remember, not everyone is as smart as you are. Students will be asking questions. They want to know why certain aspects of this proof are true. Thanks for the feedback anyway.

    • @TH-mx5ek
      @TH-mx5ek 8 років тому +3

      Ian Sergeant You're more than welcome to set up your own UA-cam channel and start sharing videos. No one is stopping you. 405 subscribers isn't hard to beat.

  • @madhusinghalike584
    @madhusinghalike584 6 років тому

    Y os=1

  • @mathematics.proofs
    @mathematics.proofs  7 років тому

    Hello guys, for those of you who want this proof without the hypotenuse as '1', please download my new document: mathsvideos.net/magick-6-6-fundamental-trigonometric-identities-their-proofs. It costs $2.99 to purchase and some of the proceeds from sales will help me maintain this project and work on more proofs. The more books I can purchase, the more I can develop this channel and MathsVideos.net. BTW, this document is being trialled. If you do purchase it, be sure to leave me some feedback!! Cheers!! :-D Also, if for any reason you are unsatisfied with it - I offer a 30 day money back guarantee.

  • @stevenhutton2691
    @stevenhutton2691 6 років тому +2

    I give this so-called ‘Amazing’ video (see above), 3 out of 10 for effort. It is meant to be a proof - GRAPHICAL, yet very unfortunately the algebra is performed out of sight of the explanatory diagram, which is such a shame.
    Ian Sergeant's view that it SEEMS over complicated is absolutely smack-on, but for the word 'SEEMS' which should be replaced by the word 'IS'. I should know. I studied the video with a certain degree of bafflement and bemusement. Steps 1, 2 and 3 are completely unnecessary, as are the introduced angles alpha and beta. It took me some considerable time to grasp what was being driven at. The up-loader rightly says not everyone is as smart as Ian Sergeant. Perhaps I fall into this category.
    From my lowly perspective, the perpendicular to OT (being PR) forms a right-angled triangle (POR) whose angle at O has already been established as being A. Therefore, the complimentary angle subtended at P must be --- wait for it, wait for it (some very basic trigonometry coming here) --- 90 degrees minus A.
    What could possibly, possibly, possibly be simpler than that? Thank you Ian Sergeant; at one point I thought it I was the only person who could see this.
    If students are asking questions as to why certain aspects of this proof are true, then why not make it easy for them to understand, instead of unnecessarily muddying the waters or, to quote the up-loader in his response to Mahua Dey, ‘complicating beyond necessity’?

    • @mathematics.proofs
      @mathematics.proofs  6 років тому +1

      I've taken no shortcuts. People like it. That's all that matters. I'll say this once again; there are more mathematics channels out there. I don't claim to be the high priest of the subject and I don't pretend that perfection exists. Have a good day. :-)

    • @mathematics.proofs
      @mathematics.proofs  6 років тому +1

      As my channel is making progress, I've noticed that I am getting more comments like these... It's normal. There will always be unhappy customers. If you try to please the world, you end up pleasing nobody.

    • @stevenhutton2691
      @stevenhutton2691 6 років тому

      You certainly have taken a shortcut in not mentioning why OS =1. Some students do not understand why OS has been set at 1 and have reasonably asked why this it the case. Have a good night's sleep :-) :-)

    • @mathematics.proofs
      @mathematics.proofs  6 років тому +1

      You're thinking too hard, that's the problem. Relax. And also, I've said this time and time again... It doesn't matter what the hypotenuse is... The same proof will emerge. I've shown this in my e-book "Magick 6". It's something I've explained probably about 20 times - which is why I made the e-book.

    • @mathematics.proofs
      @mathematics.proofs  6 років тому +1

      That's the beauty of mathematics... You can manipulate lengths - and the same proofs emerge.

  • @rrhh2261
    @rrhh2261 7 років тому +2

    good