Introduction to Complex Numbers (1 of 2: The Backstory)

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  • เผยแพร่เมื่อ 31 ต.ค. 2015
  • More resources available at www.misterwootube.com

ความคิดเห็น • 234

  • @bellamoon5244
    @bellamoon5244 5 ปีที่แล้ว +286

    This guy is practically my teacher. I’m homeschooled, so I get to use his TH-cam channel for 50% of my maths homework!

  • @brogcooper25
    @brogcooper25 8 ปีที่แล้ว +535

    I am an American engineer and I just watched this playlist to review some concepts. what I realized is that the American education system is seriously flawed and almost completely failed me. I even went to a private school where i completed first year calculus and yet somehow had to wait until college before I ever saw an argand diagram or a vector. some people here are even seriously trying remove algebra as a requirement to get graduation rates up. mr. woo, you are an amazing teacher and I am on to your logarithm playlist to see how else my expensive private American education failed me.

    • @Pete-Logos
      @Pete-Logos 6 ปีที่แล้ว +20

      I agree. I was lucky; my Dad was good at Algebra and Trigonometry so I caught a break. He tutored me and my friend, showed us how to find the square root of a number, by hand; he thought it ABSURD that American schools didn't teach us something so simple.But not everyone has Family or Friends knowledgeable, in Math particularly. That's when you have to rely on the school teachers & Education system and we didn't have youtube with awesome teachers like this guy, Sal Khan, Pat JMT, guy from 3Blue1Brown, Bill Shillito, etc. I graduated high school in '97, worked towards an associates in Music and CAD Design. Now I am going back for Logic/(Math.)

    • @deyurao3197
      @deyurao3197 6 ปีที่แล้ว +3

      Haha I remember doing square root of 2 by hand in high school following some wikipedia article. It was so much fun!

    • @justgame5508
      @justgame5508 6 ปีที่แล้ว +5

      Brett Cooper Wow the uk education system is better than I thought then, how can you possibly get onto an engineering degree without seeing a vector or knowing logarithms like the back of your hand. Even standard A level maths (16-17 year olds) in the U.K. has 3D vectors in. That's without choosing further maths, also did you do physics? If so surly they taught you what a vector was

    • @samb443
      @samb443 6 ปีที่แล้ว +1

      I went to a us public school, we had argand diagrams, vectors and all the other stuff.

    • @ahmadalfalasi8714
      @ahmadalfalasi8714 5 ปีที่แล้ว

      Brett Cooper .

  • @TheLunkan22
    @TheLunkan22 6 ปีที่แล้ว +388

    Would kill to have a teacher like this

    • @silentstorm9390
      @silentstorm9390 5 ปีที่แล้ว

      me2

    • @AlumniQuad
      @AlumniQuad 5 ปีที่แล้ว +8

      I would resurrect to have a teacher like this

    • @JJPMaster
      @JJPMaster 4 ปีที่แล้ว

      giuseppe3010 i think he ignored you because you were describing yourself

    • @jonathanmorocho6898
      @jonathanmorocho6898 4 ปีที่แล้ว

      nahhh

    • @eswnl1
      @eswnl1 3 ปีที่แล้ว

      Why?

  • @john_mckinney
    @john_mckinney 3 ปีที่แล้ว +35

    I wonder if you can imagine the amount of impact you have. I live in the Netherlands and my kids have profited so much from your lessons. Must be so satisfying knowing that kids all over the world are getting better in math!

  • @AvinashSingh-ym8cw
    @AvinashSingh-ym8cw 6 ปีที่แล้ว +51

    I never passed in maths coz it was boring never studied it never completed my maths homework, moreover if you can get promoted to next class even if you fail in one subject why not skip one. However this man is making me watch all his videos. You're great Eddie.

  • @reik2006
    @reik2006 8 ปีที่แล้ว +85

    Integer means "ganze Zahlen" (sometimes Ganzzahlen) in German and does translate to whole numbers. Natural numbers for instance are called "natürliche Zahlen".

    • @Tarrasq-Eredar
      @Tarrasq-Eredar 4 ปีที่แล้ว +5

      he had a mistake there, you wonder how someone understands math so good but fails to use google translate, we all are flawed in a way. Non the less very nice video

  • @browniesnofrownies4843
    @browniesnofrownies4843 5 ปีที่แล้ว +9

    You’re an excellent teacher. I’m continuing to find myself even more lucky, as these concepts just make sense in my head. I just watched your calculus part 1 and 2 videos and it doesn’t seem nearly as hellish as many of the people I know describe it to be. I haven’t felt challenged much at all all the way through pre-calc. I plan on taking calculus my senior year of high school and I’m beyond excited. Hopefully I’ll actually have to put more thought into what I’m doing. I love math; I always have and always will. Not many people do, but I know that teachers like you give a sense of hope and understanding to people who don’t like math, something I fortunately have always had that I consider to be a gift.

  • @kurodragon7
    @kurodragon7 6 ปีที่แล้ว +125

    I feel like I;m getting addicted to Math. How outrageous is that?!

  • @aishwaryajangir2909
    @aishwaryajangir2909 5 ปีที่แล้ว +13

    now, fortunately I'm on right channel after all these years of my life !!
    now I'm learning maths :))
    wooooohoooo!! Eddie
    god bless you for being such a perfect teacher !

  • @tomboytomgirl5356
    @tomboytomgirl5356 5 ปีที่แล้ว +6

    Prof. Woo: An exemplary professor. Thank you, so, much.

  • @bigrockets
    @bigrockets 5 ปีที่แล้ว +13

    l wish I would have had a math teacher like this in college. Eddie you are amazing!

  • @jojowolf6826
    @jojowolf6826 2 ปีที่แล้ว +5

    Wish I had a teacher like you! The way you‘re teaching it, maths really feels like a fun game!
    6:42: Anyways I’m from Germany and just wanted to mention that „Zahl“ (German) actually means number, not counting. „Zählen“ would mean counting.

  • @samikshagurung2447
    @samikshagurung2447 2 ปีที่แล้ว +4

    the hard work and effort you put in to make your students understand👏👏. You remind me of my maths teacher in
    highschool , he too was so dedicated and probably the best teacher I have ever had .

  • @haroldasraz
    @haroldasraz ปีที่แล้ว +2

    This is a very elegant and straightforward explanation of an essential mathematical concept.

  • @kyriakabeya5911
    @kyriakabeya5911 5 ปีที่แล้ว +1

    You're such a great teacher! I actually really love this.

  • @bilalkhares9337
    @bilalkhares9337 5 ปีที่แล้ว +2

    Great teacher, I am a physics undergraduate and use this video if I forget why I love maths :)

  • @alphaibrahimbarrie9195
    @alphaibrahimbarrie9195 ปีที่แล้ว

    Hi, I am an engineering student from Sierra Leone, ur class's really help me thanks very much

  • @garydunken7934
    @garydunken7934 6 ปีที่แล้ว +29

    Australia's popular maths teacher.

  • @lalhruaitluangic8337
    @lalhruaitluangic8337 6 ปีที่แล้ว

    What a fortunate time to have you tube to have the opportunity to watch this valuable video.

  • @laurensdehaan2202
    @laurensdehaan2202 ปีที่แล้ว

    This guy is such a JOY to watch! As Bella Moon implies, this kind of content can likely make home schooling viable. However, since school is only PARTLY about formal education, it's not enough for a developing child.

  • @jonathanvermeul2261
    @jonathanvermeul2261 4 ปีที่แล้ว +4

    Arabic numbers like we use today are slightly modified figures that show corners you can count. For example the 2 looked like a Z and it has 2 corners.
    Scott Flansburg shows this in one of his video's. He's the Guinness Book of Records fastest "Human calculator".

  • @SalutLunar
    @SalutLunar 4 ปีที่แล้ว +4

    I love how Eddie says he's going to take a big step back before proceeding to step forward

  • @oedesse
    @oedesse 6 ปีที่แล้ว +78

    Z stands for "Zahlen". That doesn´t mean counting. It means numbers. "Zählen" means counting. By the way: great Videos!

    • @chennebicken372
      @chennebicken372 3 ปีที่แล้ว +1

      But „Zahlen“ actually also means „to pay“.🧐

    • @1denisdenis
      @1denisdenis 3 ปีที่แล้ว +3

      @@chennebicken372 zahlen means to pay, Zahlen means numbers(plural), Zahl is number. All nouns in German are capitalised. Verbs on the other hand are not

    • @reubenmanzo2054
      @reubenmanzo2054 2 ปีที่แล้ว +1

      @@1denisdenis Yeah, the Germans love to capitalise on their nouns.

  • @vernon249
    @vernon249 9 หลายเดือนก่อน +1

    Thanks to your videos is the reason why is maths is easy .

  • @user-yh6tf6ne4s
    @user-yh6tf6ne4s 3 ปีที่แล้ว +2

    Great teacher! Thank you! Your enthusiasm makes one want to understand the explanation.
    and the explanation was so good that it created not just understanding but enthusiasm in me. I learned more and I learned deeper about complex numbers from you than all my college professors combined.

  • @charityrotich3287
    @charityrotich3287 2 ปีที่แล้ว +1

    Hea in Uganda my tr just hinted on the topic..I am thankful coz he is my new teacher😊😊😁

  • @dayashankarsuresh57
    @dayashankarsuresh57 3 ปีที่แล้ว +7

    In lockdown: I am just enjoying the study here with class like noises. 😌

  • @lunathestrnge8172
    @lunathestrnge8172 2 ปีที่แล้ว

    Thank god you exist. Without you I would have failed my test!

  • @AlessandroZir
    @AlessandroZir 2 ปีที่แล้ว

    oh, this is very intuitive and straightforward; thank you!!

  • @petten33
    @petten33 4 ปีที่แล้ว

    This is a teacher. This person is awesome. This dude is effen good.

  • @grainfrizz
    @grainfrizz 6 ปีที่แล้ว +8

    Subbed because of the beauty of your accent. Anyway, what course is this?

  • @braungebranntesmarshmallow9173
    @braungebranntesmarshmallow9173 5 ปีที่แล้ว +7

    Well I'm german and i wath these videos to improve my mathematical skills. I love your way of teaching. In germany its just a teacher asking and asking a LOT of irrelevant questions to us which basically makes our grades. You are telling so much information and the students just answer what they think so that you can comment on that. Until that video i did not even know that the Z stands for Zahl. (I think you said it means counting but actually it means number. not sure if you really said that) I love your vids! Keep going!

    • @mawley3266
      @mawley3266 5 ปีที่แล้ว

      Braungebranntes Marshmallow Same omg

  • @tuqann
    @tuqann 2 ปีที่แล้ว +1

    Al-Gaber "الجبر" is an ancient Arabic word that roughly translated to "inference from hidden truth" which came from the Islamic scholars who invented it and understood the principle connections between groups of numbers in a "formula".
    What's also interesting to note is that Algorithm comes from the Latinization of the Persian scholar Al-Khawazimi who pioneered the mathematical concepts that lay the foundations for the Turing test.

  • @JabbaWockeez_
    @JabbaWockeez_ 5 ปีที่แล้ว +2

    i've had good teachers in math. and i was gifted with easy understanding in math until a certain point lmao. But what amazes me with Eddie Woo, it's his enthusiasm. Is he teaching math like that, every day, to every class ? Or is he kind of a consultant that makes few presentations to classes?

  • @cosminduna3771
    @cosminduna3771 5 ปีที่แล้ว +2

    Is this school real? With such professors most students will become scientist and humanity will evolve a lot. Thanks Mr. Woo, you give us hope. Unbelievable!

  • @kookooburu
    @kookooburu 6 ปีที่แล้ว +2

    No idea what age group you teach Mr. Woo, but I'm a 3rd year Chemistry Masters student and find your videos very useful and still learn new stuff by watching them. You have very lucky students!

    • @newcastlensw
      @newcastlensw 4 ปีที่แล้ว

      Mr Woo is a high school teacher in a public school in Sydney, Australia.

  • @sanju5914
    @sanju5914 5 ปีที่แล้ว +2

    i am hooked to your videos sir

  • @philbowflaggon8363
    @philbowflaggon8363 8 หลายเดือนก่อน

    I got a warm fuzzy feeling at the 1, 2, 3 part.

  • @JM-jc1vz
    @JM-jc1vz 4 ปีที่แล้ว

    Great educator.

  • @graham2954
    @graham2954 10 หลายเดือนก่อน

    This guy needs to be spoken about in the same context as David Attenbourgh. His students don't really deserve him.

  • @ali-k
    @ali-k 5 ปีที่แล้ว

    Such a chill dude

  • @rohitkumarapu9825
    @rohitkumarapu9825 4 ปีที่แล้ว

    this is nice the explanations are great

  • @h1natakaho62
    @h1natakaho62 4 ปีที่แล้ว +7

    Zahl“ doesnt mean „counting“ but actually just means „number“. counting would be „zählen“

  • @khaledchatah3425
    @khaledchatah3425 5 ปีที่แล้ว +1

    Algebra was introduced by the Arabian mathematician Al Khawarezmi he also introduced the unknown number x and made the second power equations

  • @tuqann
    @tuqann 2 ปีที่แล้ว +1

    one correction: the "anglo" numbers used don't count the lines, they count the angles. which is why the number 1 has a short line ticked on the main line. these originally were Arabic number script which Europe transitioned into during the renessance period, while Arabs steadily moved to use Indian number scripts, as they dove into the concept of zero from the ancient texts of Indian scholars centuries ago when trade routes were established at the end of the Islamic Empire's conquest age.

  • @christophrenner1330
    @christophrenner1330 6 ปีที่แล้ว +6

    I'm not studying maths, but man you make it interesting

  • @brunomello7499
    @brunomello7499 2 ปีที่แล้ว +1

    I remember that when I was at primary school I used to call the integers set "Zintegers" in order to remember the symbol

  • @shahnazshaukat7253
    @shahnazshaukat7253 6 ปีที่แล้ว

    Great... Love from india

  • @garychap8384
    @garychap8384 5 ปีที่แล้ว +1

    Is there a reason that Quaternions don't feature in the Fundamentals?
    Is it just that they don't resolve a contradiction or inconsistency in the prior art?
    If so, how do we know that we have all of the fundamental operations. After all, one could say that addition and it's inverse, subtraction, implied the negatives - and then stop, calling number theory complete.
    When we added multiplication, its inverse implied the reals. But again, we could have stopped there and called it complete.
    So, do Quaternions truly not belong in the evolution of number? Is there an operation we're not considering which implies them?

  • @fatimahaltaie3319
    @fatimahaltaie3319 3 ปีที่แล้ว

    How amazing teaching

  • @tinayanebanda6961
    @tinayanebanda6961 5 ปีที่แล้ว +1

    love how he's so clear!!!!! thank you !!!!

  • @davidshechtman4746
    @davidshechtman4746 ปีที่แล้ว +1

    So the principal square root of 4 is two. But we recognize that there are actually two possibilities, two or negative two. Clearly the relationship going backwards from the creative process of geometric combination is not functional in terms of passing a vertical line test. In the case of (rectangles and squares drawn in the second and fourth quadrant) negative four we have either 2 × -2 or -2 × 2. There is no reason for imagined numbers. There are no inconsistencies in the recognition of alternately signed numbers being possible factors in the geometric composition of binomially factorable rectangles. The complex plane has been fruitful certainly. But the simplest way to analyze factors of squares is to be consistent with the Cartesian model.

  • @alphaibrahimbarrie9195
    @alphaibrahimbarrie9195 ปีที่แล้ว

    Can u upload calculus Differentiation involving logarithm and trig founction of integration

  • @sjiscgemingpeapol5294
    @sjiscgemingpeapol5294 ปีที่แล้ว

    Best Teacher

  • @piyushgautam7142
    @piyushgautam7142 3 ปีที่แล้ว

    Had all concepts of complex numbers covered hare

  • @soumyaranjanpanda5374
    @soumyaranjanpanda5374 5 ปีที่แล้ว

    Sir plz...... make a better playlist of whole complex analysis

  • @miguelpires7380
    @miguelpires7380 2 ปีที่แล้ว

    You are amazing ! Thanks (Portuguese subscraiber)

  • @uniqueh5203
    @uniqueh5203 2 ปีที่แล้ว

    The only math teacher that makes you believe that math is science as well and just a set of rules.

  • @Liwet.
    @Liwet. 4 ปีที่แล้ว

    Do you have to put +/- before a square root symbol? Doesn't the square root symbol already mean that the answer will be plus/minus?

    • @itachi6336
      @itachi6336 4 ปีที่แล้ว

      I'm assuming you know now ?

  • @Dunkelelf3
    @Dunkelelf3 9 หลายเดือนก่อน

    Zahl in german means number. counting would be zählen (yes with the umlaut) don't say zahlen and ignore the dots because zahlen would mean paying. lol. never thought about it but it kinda makes sense to have these roots in those words.

  • @andrewgonzalez7143
    @andrewgonzalez7143 6 ปีที่แล้ว +13

    Actually the Arabic numerals reflect their own values based upon how many non-obtuse angles are needed to write the numeral, NOT how many straight lines there are. Look up the first writings of Arabic numerals, and you'll see plenty of diagrams that show this.

    • @vbmendrot1
      @vbmendrot1 6 ปีที่แล้ว

      Kirigaya Kazuto what about 9, It doesn't have 9 angles , could you share where did you take that information? Because It seems not true

    • @peterfireflylund
      @peterfireflylund 6 ปีที่แล้ว +1

      That's known to be a myth.

    • @janglestick
      @janglestick 6 ปีที่แล้ว +1

      no its not exactly a myth, it's just that as you go higher in quantity different systems contributed and were absorbed. You can find many versions of the number 9, some of which attempt to make the system work. The symbology changes. For example, the number 7 with the line drawn through the middle (which isnt in the txt char) is essentially the center of the number 4 with a triangle on top, 4 + 3. There are some very peculiar versions of 9, almost all had the same middle dash as the 7, and most had many more little dashes added. It seems to follow the same set of 'rules' as the 5 and 6. Another way to see the system is that you are confirming the tokens in a trade. Someone places tokens / coins on the ground, and you draw a line around them, confirming the tally, using the shape of the numeral.

    • @unsharded8503
      @unsharded8503 5 ปีที่แล้ว

      Indian?

    • @khaledchatah3425
      @khaledchatah3425 5 ปีที่แล้ว +1

      @@vbmendrot1 the number 9 was writen a square and 2 perpendicular lines attached to it if u wrote it u can see the 9 angle

  • @jflow5601
    @jflow5601 4 ปีที่แล้ว

    very nice.

  • @pochorooster6370
    @pochorooster6370 2 ปีที่แล้ว

    Is there any formula that will create sound out of silence?

  • @pochorooster6370
    @pochorooster6370 2 ปีที่แล้ว

    How rational is it to practice irrational methods?

  • @elmariajin744
    @elmariajin744 ปีที่แล้ว

    When a teacher is too handsome and teaches flawlessly

  • @WhatIsThisAllAbout
    @WhatIsThisAllAbout 4 ปีที่แล้ว

    this video should also be under philosophy course curriculum (if theres one)

  • @sepatumerah-ff8ef
    @sepatumerah-ff8ef 9 หลายเดือนก่อน

    thank you for good the video

  • @smithmeister
    @smithmeister 3 ปีที่แล้ว

    Man I wish I had TH-cam in the 90s to save me from shitty, turgid teachers. God bless the democratisation of knowledge, and God bless you, Mr Woo!

  • @zainab-yo9fu
    @zainab-yo9fu 3 ปีที่แล้ว

    great!!

  • @sidskywalker8423
    @sidskywalker8423 4 ปีที่แล้ว

    I Agree!

  • @NeTfLeXr6s
    @NeTfLeXr6s 4 ปีที่แล้ว +1

    Hei Eddie! Small correction from ze germans: "Zahl" actually just means "number" in german :D

  • @MathHunter
    @MathHunter 2 ปีที่แล้ว

    My math teacher is your fan :)))

  • @durchschnittlich
    @durchschnittlich 6 ปีที่แล้ว +12

    Zahl doesn't mean counting, it means number. Zählen means counting

  • @brijeshgurung8300
    @brijeshgurung8300 3 ปีที่แล้ว +1

    would love to be in your class

  • @ashumishra10-a34
    @ashumishra10-a34 ปีที่แล้ว

    Sir can you teach to find zeroes of cube root of 2

  • @47Mortuus
    @47Mortuus 5 ปีที่แล้ว

    6:43
    "Zahl" means "number", not "counting"

  • @cheonsalee5118
    @cheonsalee5118 3 ปีที่แล้ว

    If I had a teacher like him, i wouldn't ave dropped maths.

  • @Judexy22
    @Judexy22 8 ปีที่แล้ว

    Hi Eddie !
    Thanks for your Videos ! Good for my revisions. It is true the saying : " What you do not use, you lose " .
    1. Have Numbers been created/invented by Man. I think so.
    2. Are Mathematics created / invented by Man or Mathematics were / are discover able ? Personally, I think that Mathematics were / are discover able.
    2. This debate has brought God into it ! Did God created Mathematics ? Obviously, no one could prove the existence of God, but it is only a belief because Humans are not use to Things falling from Nothing. So, the belief that God created all Things.
    What is of immediate interest is my Question in 1. above. Are Mathematics created / invented by Man or Mathematics were discovered by Man ?
    Thank you.

    • @mymentor7908
      @mymentor7908 6 ปีที่แล้ว

      Mathematics is discovered and tricks are invented by human. Let consider the circle, it exists in nature before we human find its credentials and equations where you can solve the equation in more than one way is the trick to tackle the problem. We humans just take-off the dust from the hidden truths. as much i understand.

  • @uscrktz
    @uscrktz 5 ปีที่แล้ว +1

    Zahl is Number and zählen is counting ;)

  • @pochorooster6370
    @pochorooster6370 2 ปีที่แล้ว

    Can math make something impractically redondant valid?

  • @silvankohler2643
    @silvankohler2643 4 ปีที่แล้ว +1

    BTW Zahl means Integer

  • @jamarkinard1090
    @jamarkinard1090 6 ปีที่แล้ว

    I do cause you can have a number in your possession without it being there..

  • @kasperadamson4654
    @kasperadamson4654 3 ปีที่แล้ว

    Nambaaa

  • @sinagholamimalek5569
    @sinagholamimalek5569 2 ปีที่แล้ว

    great

  • @dealcraftyt
    @dealcraftyt ปีที่แล้ว +1

    6:45 I really love your videos but the Z which stands for ”Zahl”, doesn’t translate to “counting”. The German word “Zahl” basically means Number/Integer as it is a synonym for “Nummer” (English: Number). The German word for counting would be “zählen”. I just had to mention it, sorry😅

  • @Davidexolover
    @Davidexolover ปีที่แล้ว

    Wish my math teacher was like him or him

  • @redmichar2409
    @redmichar2409 6 ปีที่แล้ว +5

    You are great Mr woo but seriously those students of yours are really disturbing and unrespectful

  • @denisnchemba1018
    @denisnchemba1018 2 ปีที่แล้ว

    Why you assume 3 and 5 in complex numbers

  • @pochorooster6370
    @pochorooster6370 2 ปีที่แล้ว

    How Is half of sound different from sound?

  • @mawley3266
    @mawley3266 5 ปีที่แล้ว +7

    Is it creepy that my teacher introduced complex numbers in exactly the same way?

    • @adarshvenkateswaran795
      @adarshvenkateswaran795 3 ปีที่แล้ว

      Probably watcyed this video. Seeing how positive this guys feedbsck is, a teacher would probably want to teach the same way

    • @sujeetkumarsingh511
      @sujeetkumarsingh511 3 ปีที่แล้ว

      @@adarshvenkateswaran795 Ha bhai tu sahi bol raha hai
      teacher to baccho bas padhai mein interest dilana chahte hai

  • @pochorooster6370
    @pochorooster6370 2 ปีที่แล้ว

    Do re MI fa sol la ti are different. Can you have half A sound?

  • @likemath.
    @likemath. 11 หลายเดือนก่อน

    Bạn dạy về cái gì đó của toán❤❤❤

  • @ramyavisani4104
    @ramyavisani4104 2 ปีที่แล้ว

    Where is he teaching in the video?

  • @matthewvicendese1896
    @matthewvicendese1896 4 ปีที่แล้ว

    Eddie, you're not holding back that you're in the numbers are invented camp.

  • @komalsingh9248
    @komalsingh9248 3 ปีที่แล้ว

    Came after just after i saw him in ted ex video

  • @WhatIsThisAllAbout
    @WhatIsThisAllAbout 4 ปีที่แล้ว

    I love you

  • @spakes9280
    @spakes9280 3 ปีที่แล้ว

    The german word Zahl acctualy means number and not counting ^^

  • @fabianlieret577
    @fabianlieret577 3 ปีที่แล้ว

    Zahl=Number and zählen=counting

  • @HattoriManzo
    @HattoriManzo 5 ปีที่แล้ว +8

    That "haha" was really....meh!

  • @svetlana8338
    @svetlana8338 ปีที่แล้ว

    Zahl means number