Linear subspaces | Vectors and spaces | Linear Algebra | Khan Academy

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  • เผยแพร่เมื่อ 30 พ.ย. 2024

ความคิดเห็น • 301

  • @AdhikariMohan
    @AdhikariMohan 11 ปีที่แล้ว +85

    Amazing..I spent past 7 hours trying to understand subspaces from my notes with no success and now its crystal clear in just 23.5 minutes. A huge THANKS to You!!

  • @tauceti8341
    @tauceti8341 9 ปีที่แล้ว +430

    + V is a subspace (0-6:00)
    - V contains the 0 vector: (2:26-2:44)
    - Closed under multiplication: (2:47-4:23)
    - Closed under addition : (4:28-5:35)
    Subspace 3 points ; subspace & closure under (A & M)
    Examples using concepts:
    proving a subset (S) is/not a subspace - (08:55-14:17)
    Span (v1, v2, v3) is a valid subspace of R^n? - (14:21-19:42)
    Visualizing if a simple vector can be a subpsace. U = span([1, 1]) (19:43)

    • @blakiwhite5664
      @blakiwhite5664 8 ปีที่แล้ว +43

      +Tau Ceti The world needs more people like u

    • @txuezea4072
      @txuezea4072 3 ปีที่แล้ว +1

      Thanks

  • @VineetontheBeat
    @VineetontheBeat 12 ปีที่แล้ว +31

    This is so good. Teachers usually go straight into complex examples and totally roll over the concepts. You make the concepts clear and concise. Thanks so much!

  • @Shy_Guy11
    @Shy_Guy11 11 ปีที่แล้ว +25

    In addition to that, he is great at explaining all these concepts to people who have little or no idea about the subject. Most people don't realize this, but this is extremely difficult to do for most people, but he is able to get into the mindset of a person who is new to this stuff, and explain it in such a way despite his great understanding of the subject. Thank you Sal for all your hard work..

    • @rahulkiroriwal8779
      @rahulkiroriwal8779 3 ปีที่แล้ว +1

      hello there , how are u . its been 8 years

    • @romeo5239
      @romeo5239 9 หลายเดือนก่อน

      ​@@rahulkiroriwal8779 now 11

  • @ypenburger
    @ypenburger 11 ปีที่แล้ว +157

    me looking in my linear algebra book: dafuq???
    me looking in the same book after a video from khanacademy: Aha!

  • @yangvely7018
    @yangvely7018 7 ปีที่แล้ว +559

    You are better than my professor lol. I dont know why I attend college.....

    • @7thFormVoid
      @7thFormVoid 6 ปีที่แล้ว +37

      So you can get a real degree?

    • @That_One_Guy...
      @That_One_Guy... 5 ปีที่แล้ว +23

      Yeah, to get degree so you can get a job, that's so annoying

    • @Nomnomnom165
      @Nomnomnom165 5 ปีที่แล้ว +14

      @@That_One_Guy... I'm in college and the companies I'm aiming for don't need degrees. They're just insanely hard for everyone to get into

    • @codingtheworld674
      @codingtheworld674 5 ปีที่แล้ว +10

      If you are just learning mathematics in your college, so you don't need to go. We should not be in college just for a degree paper, do more things(-like starting a new projects,etc.)...

    • @daehwankim4246
      @daehwankim4246 5 ปีที่แล้ว +1

      ㅇㅇ

  • @lolalukie713
    @lolalukie713 12 ปีที่แล้ว +23

    you accomplished in 23 mins what my linear algebra prof couldn't in two 2 hour lectures.

    • @rahulkiroriwal8779
      @rahulkiroriwal8779 3 ปีที่แล้ว +2

      hey how u doing , its been 8 years ?

    • @lolalukie713
      @lolalukie713 3 ปีที่แล้ว +17

      @@rahulkiroriwal8779 I have my degree in Mechanical Engineering and am working as a project engineer for construction projects and have started a business on the side ! Thanks for checking :D

    • @bookman9897
      @bookman9897 3 ปีที่แล้ว +3

      @@lolalukie713 wow really great keep growing

    • @mihnea4924
      @mihnea4924 หลายเดือนก่อน

      @@lolalukie713 how about now , you good ?

  • @dalisabe62
    @dalisabe62 2 ปีที่แล้ว +3

    I love his style and voice. His detailed persistent explanations show how much he is capable of relating to his audience and how much experience he has in teaching. I found him the best explainer that is out there for concepts that are typically confusing or need further breakdown.

  • @cwruhsk5
    @cwruhsk5 14 ปีที่แล้ว +2

    Wow..... I spent five hours trying to learn this, and still could not comprehend the material. 20 minutes of this video, and everything makes sense now. This is awesome!!!

  • @devilpizza123
    @devilpizza123 13 ปีที่แล้ว +1

    thanks! my lecturer is terrible at explaining this stuff and uses all the extremely abstract notation stuff that no body understands. your explanations are easy to understand and make difficult to grasp concepts simple. i love it!

  • @Sundoren
    @Sundoren 10 ปีที่แล้ว +15

    superb voice superb explanation superb colors why we dont have teachers like u damn

  • @Hemenmyname
    @Hemenmyname 10 ปีที่แล้ว +20

    I personally am thankful for your service sir, thank you very much.

  • @TheBananahulk
    @TheBananahulk 9 ปีที่แล้ว +181

    Haha if you look at the statistics. The viewer count always goes up before exam periods :P

    • @laartisticfellow2382
      @laartisticfellow2382 5 ปีที่แล้ว +2

      Im a student of statistics and i can vouch for that

    • @Iluminent
      @Iluminent 5 ปีที่แล้ว +4

      crazy thought you got there, I wonder why that is...

    • @Xxjorgex123
      @Xxjorgex123 5 ปีที่แล้ว +9

      how you figured that out genius?

  • @neomarc9946
    @neomarc9946 7 ปีที่แล้ว +27

    Thank you sir for making it 100% easier. My professor sucks af.

  • @LAnonHubbard
    @LAnonHubbard 14 ปีที่แล้ว +5

    Very cool explanation. I've been trying to teach myself this sort of stuff from books and Wikipedia. They're too dry for my current level of knowledge. Your dynamic presentation is exactly what I need and I'm sure will help me to understand other resources.

  • @fukgovernment
    @fukgovernment 10 ปีที่แล้ว +62

    You deserve a noble price. Thanks

    • @anonymoose8829
      @anonymoose8829 10 ปีที่แล้ว +12

      Nobel Prize? :P

    • @inteusproductions
      @inteusproductions 10 ปีที่แล้ว +29

      Nolen Lah Nope, just a noble one

    • @Sundoren
      @Sundoren 10 ปีที่แล้ว +1

      inteusproductions :DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD

    • @StephenRayner
      @StephenRayner 10 ปีที่แล้ว +2

      inteusproductions Haha, he sure does, but none are given for teaching.

  • @snake10566
    @snake10566 11 ปีที่แล้ว +3

    The way you define everything in simplistic terms is amazing. Thank you so much.

  • @Hepichack
    @Hepichack 10 ปีที่แล้ว +5

    Congratulations man !!!
    They way you teach is very clear-easy-good,not only because you explain them with great way,but because you used examples,and you used Cartesian plane to show how vectors works in reality. That really helps,because to understand something in maths,you need to implement it. Keep the good job !!!

  • @enjoyablesounds
    @enjoyablesounds 14 ปีที่แล้ว +1

    Thank you sal, you are a great example of a good human being. With all negativity around the world you give me hope. Thank you so so much :)

  • @0dablkin0
    @0dablkin0 11 ปีที่แล้ว +3

    Thank you very much, my professor is blowing through this information leaving me wondering what just happened, you are helping me keep pace with the lessons

  • @fuzzybuns1234
    @fuzzybuns1234 10 ปีที่แล้ว +10

    Hey Sal,
    I looooove your videos, first of all. After taking Algebra 1 I told myself I would spend one summer learning all through Calc 1, and, thanks to you, this summer I am attending SacState as a Freshman in high school. I know that this topic is unrelated to the video and that you probably won't even have time to read this, but I was wondering if you have any intuition that you could teach me regarding visualization of Lie groups and symmetries because it's really difficult for me to imagine. I understand how group theory works, but imagining these things as circles and large manifolds is a giant leap from just sets of numbers. Thanks a ton for your videos; I don't know what I would have done without you.

    • @awesomecodeyay8382
      @awesomecodeyay8382 2 ปีที่แล้ว +1

      Nice, I did calc 3 and Diff Eq in 8th grade. I also attended USAMO.
      Are you a full time student at the university, or are you just taking some courses there? I don't think you can graduate high school right in just one summer. Also, I'd imagine that there are gaps in your mathematical knowledge because you haven't done enough geometry, and you did not spend enough time on the prerequisites of calc.
      Additionally, doing higher math does not mean a lot. I did Calc BC in school as a 7th grader, and I don't consider my 7th grade self all that smart. Doing calc does not require as much creative thinking as math competitions.
      Try the first competition to the IMO, which is the AMC 10/12. Try some problems there and see how you do. This competition will probably be hard for someone without much experience. Next, there will be the AIME, which is much much harder. If you want to be better at math, I suggest participating in these competitions.

  • @makavelic2000
    @makavelic2000 11 ปีที่แล้ว +1

    I LOVE YOU. This helped so much. was freaking out about this class and was about to drop it, but now i understand enough to not panic.

  • @bryancolon5090
    @bryancolon5090 3 ปีที่แล้ว +4

    Thank you so much. When you stated between 5:10-5:30 that we're simply choosing vectors within the given parameters of our space V and then adding them together to see if the resultant vector was still in space V, everything finally clicked. I immediately understood what "closed under addition" and "closed under scalar multiplication" meant. Words cannot describe my gratitude! Thank you!

  • @fuahuahuatime5196
    @fuahuahuatime5196 11 ปีที่แล้ว

    Wow, thank you SOO much! My teacher did a HORRIBLE job explaining this. I've tried searching everywhere on youtube... Thanks man! Seeing it visually helps a lot more than just seeing the theorems or whatever proven with random variables with no significance.

  • @abdulrahman226
    @abdulrahman226 12 ปีที่แล้ว

    dude, Partrick is good and khan is good, they r different in their styles. khan is the very best in explaining the derivation and the origin of things, partick is gr8 in solving examples.

  • @sauryashrestha
    @sauryashrestha 8 ปีที่แล้ว

    I highly recommend this video. The presence of a graph makes it much easier to comprehend!

  • @deathmachine91
    @deathmachine91 11 ปีที่แล้ว +2

    You are a better teacher than my professor. Thanks for putting the video up

  • @EchoL0C0
    @EchoL0C0 11 ปีที่แล้ว +1

    Thank you so much for taking the time to make this video! I really appreciate the fact that you take the effort to try to connect these concepts in many different ways, like in terms of things we've already learned, or what works and what doesn't, instead of just the formal mathematical definition. I mean, appreciate the formal mathematical definition, (I like math because it seeks "truth without error") but it's not much use if I don't understand things in the first place. Anyway, thanks!

  • @SoloPro
    @SoloPro 9 ปีที่แล้ว +1

    Seriously this explanation was good im so happy i typed it in youtube... defo liked and subbed

  • @beanfant_jesus
    @beanfant_jesus 5 ปีที่แล้ว +1

    You taught me in 25 minutes what my professor took 2 hours to cover in class. Thank you!

    • @codingtheworld674
      @codingtheworld674 5 ปีที่แล้ว +1

      it is not the first time you have been facing like that a new subject, so that you understood in 25 min.

  • @ocsantiago
    @ocsantiago 14 ปีที่แล้ว +2

    This is great. I just discovered your library as well. Great stuff!!

  • @aandha1
    @aandha1 13 ปีที่แล้ว

    This guy is just unbelievale !! Thumbs upp!!!

  • @rapid1010
    @rapid1010 6 ปีที่แล้ว +1

    You're presentations are very clear and you're a great teacher as well.Thank you very much for these videos!

  • @MrSauce714
    @MrSauce714 13 ปีที่แล้ว

    Linear algebra test tomorrow not worried about this topic thanks to you!!!! Great vid!!

  • @alejandromunoz8086
    @alejandromunoz8086 6 ปีที่แล้ว

    You explained to me in under half an hour wait University professor can't explain in 3 lectures. Thank you so much, I understood a hole section in this video

  • @stephaniepaul2010
    @stephaniepaul2010 11 ปีที่แล้ว

    crazy to think i'm paying £9k a year tuition fees, but learn the course from these videos! Thankyou! :)

  • @phalgunvedantam1388
    @phalgunvedantam1388 6 ปีที่แล้ว

    Thanks to sal i now understand everything about basis, vector spaces and every other thing right before my tomorrow's exam... Thanks sal

  • @nturner4
    @nturner4 14 ปีที่แล้ว

    wow this is awesome. this is SO much more helpful than any lecture I've been to this year!

  • @danielgibbons301
    @danielgibbons301 4 ปีที่แล้ว +1

    CLEARLY!

  • @preciousgeofrey6192
    @preciousgeofrey6192 ปีที่แล้ว +1

    More gratitudes should be granted to you Sir

  • @IndulgeObscenity
    @IndulgeObscenity 14 ปีที่แล้ว +1

    You are truly a great teacher! Than you for the posting!

  • @swagatggautam6630
    @swagatggautam6630 2 ปีที่แล้ว +1

    After watching this video I just have the urge to show this to my Linear Algebra lecturer and ask him, why his explanations are not this simple to understand?????????????????????????????????????????????????????????

  • @nqvietanh343
    @nqvietanh343 13 ปีที่แล้ว

    If I have Khanacademy on youtube, what is the point of staying in my math class? Well, I have more time to study other classes! Yay!

  • @danielgonzalezisaiev9643
    @danielgonzalezisaiev9643 12 ปีที่แล้ว

    I'm learning crazy much! You already feel like my best friend dear khan academy mystery man.

  • @cnjaify
    @cnjaify 12 ปีที่แล้ว

    thank you sir. u should receive like a humanitarian award for the number of times u have saved my life lol

  • @japierdoleokurwa
    @japierdoleokurwa 13 ปีที่แล้ว

    @123aellis in example (x1 in R and x1>0, x2 in R) this will be a subspace if any c that is in real set will satisfy above conditions. Your 'c' does satisfy condition -> v[2,4]*3=[6,12]. 6 is greater than 0. However -3 will product vector [-6,-12]. -6 does not satisfy condition x1>0. Important is that it must be valid for any c's in R.

  • @homestar92
    @homestar92 13 ปีที่แล้ว

    These videos are teaching me more than my professor does. You may be saving my grade.

  • @sarveshc2985
    @sarveshc2985 ปีที่แล้ว

    wow what an amazing explanation! I spent too much time looking in notes and couldn't get much out of it

  • @eshaghazali2482
    @eshaghazali2482 5 ปีที่แล้ว +4

    I have a quiz tomorrow God bless you sal!! 😭

  • @rockclimbermaca
    @rockclimbermaca 12 ปีที่แล้ว

    Salman Khan, the creator of Khan Academy, holds a bachelors degree in mathematics, a bachelors degree in electrical engineering and computer science, as well as a masters degree in electrical engineering and computer science from MIT, and an MBA from Harvard Business School. He is unbelievably talented, so instead of complaining you should be grateful for this amazing resource that you can implement in your education.

  • @Anonymoose123456789
    @Anonymoose123456789 11 ปีที่แล้ว

    A scalar is any number contained within the real numbers, which includes zero and every single positive and negative number. That also includes all of the fractions and decimals.

  • @AdamBr-q8d
    @AdamBr-q8d ปีที่แล้ว

    You are a life saver, thank you! I fully understand it now.

  • @chvere123
    @chvere123 14 ปีที่แล้ว

    it really saved me time for understanding these materials, thanks a lot.

  • @shishenliart
    @shishenliart ปีที่แล้ว

    I think of it as a subset being an open community of vectors whereas a subspace is a closed community of vectors.
    Since you can have a subset of Rn without it being closed under multiplication or addition or having the zero vector since it can span some or all of Rn. However, to get a subspace, you have to have it be in a subset that satisfies having the zero vector, closed under addition and multiplication.

  • @oneinabillion654
    @oneinabillion654 5 ปีที่แล้ว +3

    Sometimes you question yourself the usefulness of certain concepts.

    • @7kwm
      @7kwm 3 ปีที่แล้ว

      u just got to get that answer right buddy

    • @oneinabillion654
      @oneinabillion654 3 ปีที่แล้ว

      @@7kwm oh is that how it is 🤣

  • @DEEPAKSINGHcreative
    @DEEPAKSINGHcreative 5 ปีที่แล้ว

    In summary, In order to define subspace using vector we need to define for R^n i.e. for all real value, exculding a certain ranges would bring up the possibilty of subset instead of subspace, SPAN by default are defined for R, hence they automatically fall into subspace cateogory. If there is any example that doesn't include R i.e real domain, please do provide. I think one you have mentioned would be n dimension zero vector, the addition or linear combination again results in zero vector, which is exception of trend, but for non-zero n-dimensional vector space to be termed as subspace, it needs to be defined for 'R' .
    Note: Here R represents real domain.

  • @rochelletarin6422
    @rochelletarin6422 3 ปีที่แล้ว

    Well, this made more sense than my teachers lecture. Thank you!

  • @jaker9007
    @jaker9007 3 ปีที่แล้ว

    Best tutorials on linear algebra!

  • @Andradam33
    @Andradam33 14 ปีที่แล้ว

    Making up where my prof lacks - every time. Thanks for your useful explanations and videos.

  • @michellezhuang2483
    @michellezhuang2483 4 ปีที่แล้ว +1

    For the example of whether U=span{v_1, v_2, v_3} is a subspace of R^n, don't v_1, v_2, and v_3 also have to have n components, as in they are a subset of R^n?

    • @michellezhuang2483
      @michellezhuang2483 4 ปีที่แล้ว

      Other than that, your video helped clear everything up. Thank you!

  • @techtalentblueprints
    @techtalentblueprints 2 ปีที่แล้ว

    You are great. Now this concept is clear crystal for me.

  • @예밤-f3k
    @예밤-f3k 3 ปีที่แล้ว +1

    this was such a great review before my first test

  • @j0shda116
    @j0shda116 3 ปีที่แล้ว

    I was completely lost before watching only 25 seconds on this video.
    now I am a linear algebra prof

  • @hellokat68
    @hellokat68 10 ปีที่แล้ว

    thanks so much, you help me learn all these math concepts that I were unable to grasp in class when I was in school

  • @yoursoothingmusic1754
    @yoursoothingmusic1754 3 ปีที่แล้ว

    thanks. you took 30 mins to to untwine the confusion my professor infused in me for one semester

  • @violalagonigro-m4d
    @violalagonigro-m4d ปีที่แล้ว

    Single-handedly saving my life

  • @trytwicelikemice7516
    @trytwicelikemice7516 9 ปีที่แล้ว

    Trying to think in an abstract way about subspaces... could you say that a subspace is essentially an extension of the concept of an infinite line (1 dimensional) or plane (2 dimensional) into m dimensions, m

  • @wesKokigen
    @wesKokigen 13 ปีที่แล้ว

    THanks! It makes so much sense now.

  • @A-003
    @A-003 14 ปีที่แล้ว

    Thanks you VERY MUCH for the nice, simple, useful explanation. God bless you

  • @wonkamobil
    @wonkamobil 14 ปีที่แล้ว +1

    Thanks a ton for the video, hopefully i'll pass my final because of this lol

  • @DFsdf3443d
    @DFsdf3443d 7 ปีที่แล้ว +1

    would it then be correct to say that: Any linear combinations of vectors in a subspace must be equal to a vector that is also in the subspace ?
    kind of like the closure under addition? just with linear combinations?

  • @Thonix94
    @Thonix94 10 ปีที่แล้ว +13

    that is a counter strike cross hair

    • @afakcay
      @afakcay 7 ปีที่แล้ว +1

      batuhan cakar Bunu yazsa yazsa turk yazar zaten 😂 Adamsin Batu

    • @abhinavjain2985
      @abhinavjain2985 5 ปีที่แล้ว

      Nope its a pubg crosshair

  • @aranyak1881
    @aranyak1881 ปีที่แล้ว

    Amazing, you teach 10 times better than my school does, god this world is weird.

  • @siddharthaganguly9286
    @siddharthaganguly9286 6 ปีที่แล้ว +1

    Sal really enjoyed proving 0 vector is a subspace XD , great lesson as usual , keep doing it

  • @Adam-gp3ij
    @Adam-gp3ij 5 ปีที่แล้ว

    That’s pretty clear! Thank you

  • @fathimahida8878
    @fathimahida8878 6 ปีที่แล้ว

    it really helped me... thanku soo much...keep uploading more vedios...

  • @Soccercrazyigboman
    @Soccercrazyigboman 12 ปีที่แล้ว

    u know, I wonder why i even go to my math classes anymore...
    oh wait, potential attendance quiz and knowing what to look up on Khan

  • @judyhayun1102
    @judyhayun1102 4 ปีที่แล้ว +1

    is a point(that is not equal to zero) also a subspace? If we think of it as a position vector, it actually passes through the origin. that's why I'm curious

  • @amangoel8724
    @amangoel8724 4 ปีที่แล้ว

    thanks buddy you made my day

  • @darrowshire11
    @darrowshire11 13 ปีที่แล้ว

    Perfect! Just what i needed! Thx alot

  • @teddybeitler
    @teddybeitler 14 ปีที่แล้ว

    once again, you have saved me. thank you sir!

  • @omertopchi2280
    @omertopchi2280 8 ปีที่แล้ว +1

    Thank you so much!

  • @anacousticguitar123
    @anacousticguitar123 10 ปีที่แล้ว +26

    when will i ever use this in life apart from an exam

    • @nightmare4eVerr1
      @nightmare4eVerr1 9 ปีที่แล้ว +7

      ***** its like learning all the scales on the guitar without knowing how to strum a fcking chord!

    • @franciscopadilla5350
      @franciscopadilla5350 9 ปีที่แล้ว +1

      Ahmed Adnan Exactly, you gotta start somewhere.

    • @maroseocampo6605
      @maroseocampo6605 9 ปีที่แล้ว +17

      you will use this when you teach your kids a linear algebra. hahah

    • @lu-dx6oh
      @lu-dx6oh 9 ปีที่แล้ว +7

      math is analyzing the world around us, quantifying objects and giving us a way to represent those objects using numbers, pictures, and functions.
      for example you could say a space contains all youtube videos a subspace contains all math videos a subspace of that subspace contains all of khanacademy videos a subspace of that subspace contains this video

    • @imreallygoodatlife
      @imreallygoodatlife 7 ปีที่แล้ว +22

      I'm watching this video for work right now. Cancer research. It's kind of important.

  • @dca24100
    @dca24100 12 ปีที่แล้ว

    I feel ya. We're using that book here as well.

  • @diz8344
    @diz8344 6 ปีที่แล้ว

    Thanks, it really helps me a lot.

  • @marygraceadolfo8782
    @marygraceadolfo8782 5 ปีที่แล้ว +1

    You're very kind, sir. Thanks

  • @Bumperpegasus
    @Bumperpegasus 13 ปีที่แล้ว

    And you are officially my new teacher

  • @sheralikhtk5200
    @sheralikhtk5200 4 ปีที่แล้ว

    thanks ALOT u saved me

  • @timgoppelsroeder121
    @timgoppelsroeder121 5 ปีที่แล้ว

    Thank you for these tutorials. They are very compact

  • @Ennendra
    @Ennendra 12 ปีที่แล้ว

    Bro, I know that feel.
    But this, this is definitely a lifesaver right now :D

  • @empirewhite
    @empirewhite 8 ปีที่แล้ว

    Thank you, you are the best!

  • @shaahinflamenco
    @shaahinflamenco 14 ปีที่แล้ว

    i wish my teacher was like him

  • @123aellis
    @123aellis 13 ปีที่แล้ว

    Question:
    Aren't the tests for closure for both scalar mult. and vector add. arbitrary? If you used c=3 for scalar multiplication, you would have had a new vector, still with x>0, and would answer that it is closed, and therefore is a subspace...? I'm having trouble getting my head around the idea of this...

  • @ishmaelteddy1454
    @ishmaelteddy1454 11 หลายเดือนก่อน

    I didn't know you could scale a set of vectors by 0. I always thought your scaler should always be either a positive or negative number

  • @mrdylanman666
    @mrdylanman666 14 ปีที่แล้ว

    Something just completely clicked. Thanks.

  • @kushagrakalla7933
    @kushagrakalla7933 7 ปีที่แล้ว

    It helped a lot

  • @Recordingization
    @Recordingization 4 ปีที่แล้ว

    Nice class!

  • @bsvshashanka6055
    @bsvshashanka6055 3 ปีที่แล้ว

    wah!!
    superb video

  • @TheRealChinOfKimJongUn
    @TheRealChinOfKimJongUn 8 หลายเดือนก่อน

    This explained more in 20 mins (10 with playing it on double speed) than my college prof did in an 1.25 hrs...

  • @SciFiGirl1023
    @SciFiGirl1023 15 ปีที่แล้ว

    this helped so much thank you soo much!