PROOF by CONTRADICTION - DISCRETE MATHEMATICS

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  • Опубліковано 19 гру 2024

КОМЕНТАРІ • 190

  • @squirrelsociety3318
    @squirrelsociety3318 3 роки тому +561

    I feel like understanding proofs is just memorizing as many examples as possible and hope you see them on the test because there is no way the average student can come up with this on their own.

    • @crazymathematics3263
      @crazymathematics3263 3 роки тому +9

      any student can come up with proof....

    • @alisonurfe1119
      @alisonurfe1119 3 роки тому +133

      @@crazymathematics3263 no.

    • @Chrisymcmb
      @Chrisymcmb 3 роки тому +51

      For me, I feel like it is a matter of memorizing at first, continue to practice, memorize, practice, learn something new, things start adding up, then you actually can start to develop the proofs after things kind of click in your mind. For me at least, it takes a vast amount of effort on my part to study and study until this starts to occur.

    • @cjcarani3299
      @cjcarani3299 2 роки тому +35

      @@crazymathematics3263 ratio + L

    • @treesareshady
      @treesareshady 2 роки тому +7

      It's like solving really complex trigonometric integrals. Where if you don't know all of the trig laws, the integral won't be as easily solved. I agree, there are many possibilities and it is difficult to remember them all.

  • @djgulston
    @djgulston 6 років тому +304

    I really wish I was this creative. Proofs are never easy for me.

  • @weldin
    @weldin 3 роки тому +388

    Watching these videos: Yeah, that makes sense!
    Going back to my problems from class: Totally lost.

    • @Kage1128
      @Kage1128 3 роки тому +2

      🤣🤣🤣🤣 so true

    • @Oreo_Editz
      @Oreo_Editz 3 роки тому +1

      Same :/

    • @estein11
      @estein11 7 місяців тому

      😂😂😂🤣same😭😭😭

  • @MobiusChickenStrip
    @MobiusChickenStrip 7 років тому +174

    Usually youtube explanations miss the mark, or aren't as informative as they would like to be. Your video is not one of those. It was very effective in explaining the material, and I feel like I understand it better now. Thank you!
    That being said I am NOT ready for my exam tomorrow...

    • @minhajansari8272
      @minhajansari8272 5 років тому +1

      How did your exam go?

    • @Nerfyy
      @Nerfyy 5 років тому +2

      @@minhajansari8272 he failed

    • @evans3636
      @evans3636 5 років тому +3

      @@Nerfyy eep, two years ago. Also, yeah its also the same reason I'm here now. xD damn.

    • @ronanhunt1884
      @ronanhunt1884 4 роки тому +2

      @@evans3636 me too man mine is in an hour

    • @evans3636
      @evans3636 4 роки тому +2

      @@ronanhunt1884 Hey, ya did good?

  • @shayanjavadi
    @shayanjavadi 8 років тому +72

    Hey man, you literally saved my grade in dm. I love the no bs way that you present things and I would definitely be a patron if I wasn't broke as a joke lol.

    • @Trevtutor
      @Trevtutor  8 років тому +15

      +shayan javadi Glad I could help!

  • @Chandler890
    @Chandler890 7 років тому +262

    why does this type of math exits

    • @Trevtutor
      @Trevtutor  7 років тому +97

      Well, this is one of the major proof techniques that builds mathematics. If we didn't have this type of math, we wouldn't have any math at all.

    • @lucasmartin4883
      @lucasmartin4883 7 років тому +11

      But why I do need to prove anything if its already been done?

    • @shanolinnaidoo2977
      @shanolinnaidoo2977 7 років тому +20

      This maths forms the bedrock of all computation. In essence without it we would not have any technology whatsoever. Its like someone claiming to be a programmer without knowing this math...would not be a decent programmer

    • @kureysalp
      @kureysalp 6 років тому +9

      @@lucasmartin4883 You are not learning to proof something proven. You are learning proof something that noy proven yet.

    • @LuisPereira-bn8jq
      @LuisPereira-bn8jq 5 років тому +16

      Because this is what real mathematics actually is.
      Most of what regular people call mathematics is nothing more than glorified arithmetic.

  • @Keinkrt
    @Keinkrt 3 роки тому +6

    Thank You TrevTutor For Saving Me in My Midterms. Shout out kay Rosner. Salamat sa pagsend sa GC HAHAHAHA.

  • @AndrewSmithDev
    @AndrewSmithDev 8 років тому +10

    I've been struggling with proofs but the way you explained it really helped to clarify things
    Thanks

  • @RedQueenAvenged
    @RedQueenAvenged 9 років тому +56

    I'd like to add a comment about your example with the square root of two. When saying that it is equal to a/b, you have to specify that b != 0, especially if some professors are sticklers for taking off points.
    Cheers.

    • @brindynschultz
      @brindynschultz 4 роки тому +1

      Andre Pereira you also need to specify that a and b are integers.

    • @Diaryofaninja
      @Diaryofaninja 4 роки тому

      Brindyn Schultz fax

  • @hessamesl1149
    @hessamesl1149 6 років тому +1

    I have been watching your videos on discrete math for 2 months now. You made a challenging course easy to understand and easy to follow. I wish I had seen your videos way before this. so THank you Thank you and Thank you!

  • @maurods1
    @maurods1 9 років тому +13

    Thanks, our book on applied formal logic is very confusing (mixed up examples and such) but on your channel I can almost find everything that's in there, but more concisely explained. Thanks a lot!

    • @Trevtutor
      @Trevtutor  9 років тому +4

      +maurods1 Hopefully you got what you need here :)

  • @7FlashFlash
    @7FlashFlash 9 років тому +7

    Your videos are incredibly helpful and it is very easy to understand what you are saying, thank you.

  • @dredre0702
    @dredre0702 7 років тому +5

    This class is tough! I appreciate the help

  • @mangogoose23
    @mangogoose23 7 років тому +1

    bless you sir,best and most concise videos.Unlike my professor who rambles about random things for an hour. ill donate once my internship starts next week.

  • @feldn
    @feldn 9 років тому +11

    All these videos are very helpful, thank you for sharing!

  • @gamzekoyuncu
    @gamzekoyuncu 2 роки тому

    When I was in the class, I couldn't understand the proof by contradiction. But now, it's all fine. This video made the subject clear. Thank you!

  • @KalebMicklatcher
    @KalebMicklatcher 4 роки тому +2

    I learned more in this video than I did our entire week of class, thank you!

    • @nubcops220
      @nubcops220 Рік тому +1

      I literally larned nothing

  • @DaRealSiri
    @DaRealSiri Рік тому +2

    Test tomrrow, we gonna cook it. LMAO, i am not ready, but you always gotta have the mindset you are going to get 100% am I right

  • @dorian6032
    @dorian6032 2 роки тому

    I attempted the last example at 5:15 a bit differently (please tell me if this is incorrect):
    1. Assume ( A - B ) ∩ ( B - A ) ≠ ∅
    2. Rewrite:
    = ( A ∩ B' ) ∩ ( B ∩ A' )
    = A and B' AND B and B'
    = A or B AND A' or B'
    = ( A ∪ B ) ∩ ( A' ∪ B' )
    = ( A ∪ B ) ∩ ( A ∪ B )'
    3. Rewrite: A ∪ B
    C ∩ C' ≠ ∅
    The above does not hold therefore the opposite is true.
    Is this counter-example hold true?

  • @miguelangelosuna7068
    @miguelangelosuna7068 5 років тому +2

    Thank you so much, professor, I can finally understand!

  • @youngdumbandbaroque1543
    @youngdumbandbaroque1543 7 років тому +3

    When working with rational (a / b) in any example (where both variables are integers), are you supposed to assume initially that a and b cannot be reduced?

  • @MTDueling
    @MTDueling 4 роки тому

    at 2:43 you say the only way (a•a) can be even is if "a" is even...but a negative times a negative equals an even number, so can't "a" also be negative??

  • @josejayant3127
    @josejayant3127 6 років тому +26

    I still don't understand.

  • @muhammedismail8299
    @muhammedismail8299 5 років тому +2

    What I did for (A - B) intersection (B - A) = empty set:
    Assume x is an element (A - B) intersection (B - A) where
    therefore x is an element of (A-B) and x is an element of (B-A)
    therefore (x is an element A and x is NOT an element of B) and (x is an element B and x is NOT an element of A)
    therefore contradiction

  • @lxdzii
    @lxdzii 2 роки тому +1

    this was beautiful!!!! thank you

  • @abnormalbat1966
    @abnormalbat1966 8 років тому +1

    why the hell you are so good in teaching DM !!! :') thnx man !!

  • @moatazmujahid2654
    @moatazmujahid2654 6 років тому +2

    Please , Can you explain that
    You assumed " randomly " that ( a/b ) irreducible and after that I could get a contradiction .
    But , what if you assumed that (a/b) is reducible , then you won't find any contradiction.
    Hopefully you answer me.

    • @Trevtutor
      @Trevtutor  6 років тому +2

      If I assume it's reducible, then that's not the definition of a rational number so it's not proving anything. Rational number definition is a/b where a,b are irreducible.

    • @moatazmujahid2654
      @moatazmujahid2654 6 років тому

      @@Trevtutor Thank you for your quick reply .
      It's clear now .

    • @Error-wc6vy
      @Error-wc6vy 2 роки тому

      @@Trevtutor sorry i dont quite understand that, why 2a/2b cannot be defined also as a rationale number when a/b is rational? even though 2a/2b is reducible, but is has exactly same value with a/b.

  • @mariuschritin7874
    @mariuschritin7874 3 роки тому +1

    THIS WAS BEAUTIFUL

  • @ValidatingUsername
    @ValidatingUsername 2 місяці тому

    The same kind of proof that primes are infinite by contradiction is nearly applicable to the theorem that all non prime numbers are the sum of some prime factors on the premise that once the number is surpassed by all combinations of sums of prime factors the number is the next prime added to the list of primes.

  • @hikariwuff
    @hikariwuff 4 роки тому +5

    How does this apply to real life? Like, when is someone gonna walk up to you and say "Prove that the square root of 2 is irrational"
    You don't really have to answer this, just a thought lol

    • @duniiii69
      @duniiii69 4 роки тому

      logic applies to real life pretty well. mathematical logic is not only used in mathematical proofs, or applications of mathematics, but also it can be used to deduce what is correct and what is not in real life. imagine you are -say- teacher and some kids had a fight and you want to figure out who was guilty. you ask to kids and get some responses and conclude the followings:
      If Jack is innocent, then both John and Annie are guilty
      Either John or Annie is innocent
      Either Jack is innocent or John is guilty
      Then, who is guilty?

  • @virajrana7398
    @virajrana7398 6 років тому

    Hey TrevTutor, for the proof that rad 2 is irrational can you assume rad 2 is rational thus it’s equal to a/b where b does not equal zero and a and b are integers. If you multiply rad 2 by an int. such as ‘b’ you arrive at a contradiction since ‘a’ is not an integer as you assume in the definition. rad 2 times an integer is an rational number.

  • @jarncherry4581
    @jarncherry4581 4 роки тому +3

    you're incredibly helpful but i hate this section. This is the hardest one for me so far from all discrete math. I would not be able to do a proof by myself, it seems like you need to pull stuff out of your ass to manipulate things to agree with what you want or disagree. I still don't get how to do these

  • @rachelmontgomery8667
    @rachelmontgomery8667 4 роки тому +1

    Your videos are amazing! You're so effective in explaining the material and make it much more painless. Thank you so much! Without you I would be failing this course.

  • @hikariwuff
    @hikariwuff 4 роки тому

    This is an amazing video! Couldn't you also use a venn diagram for #2?

  • @isam3l3
    @isam3l3 4 роки тому

    thank you. i like vids again! 😄

  • @coldassassin6615
    @coldassassin6615 5 років тому +1

    What level is this proof at? Like, university (college?), college (highschool?) Orr?

  • @bunnyking1997
    @bunnyking1997 2 місяці тому

    Shouldn't it be also stated at the squareroot 2 = a/b that b is not equal to 0?

  • @BaDman20051
    @BaDman20051 Рік тому

    i have a test in like 4 hours and hope this helps

  • @kingwoomy8781
    @kingwoomy8781 3 роки тому

    If rational numbers are irreducible fractions, then how can integers, whole numbers, and natural numbers be subsets of the rational numbers? If a rational number is an irreducible fraction, then wouldn't it be impossible to get a non-decimal number when thr fraction is simplified? *Would integers just be considered rational numbers whose denominator is 1, since (any integer/1) is irreducible?*

  • @MrFrazerz
    @MrFrazerz 3 роки тому

    Yes, I know: it's a super old video, but it would be advantageous to entirely use symbolic logic instead of half symbolism and half written English; For example, at 6:21, you wrote, "such that" when you could've just wrote a semicolon since they mean the same thing. It's much more concise and holds meaning in all languages. Also, one should pick a format and stick with it when writing a paper or even a proof.

  • @44jbly
    @44jbly 7 років тому

    What software do you use?

  • @RomanHold
    @RomanHold 2 роки тому

    A proof of contradiction is just showing you that the opposite of something that is an infinite set, is a moebiusstrip, which is "as limited as possible" (it is a mathematical object that defines what irrationality is), because it has only one surface and one edge, therefore it also is the collatz conjecture in two different ways and not and because this is not congruent with the theorems of the classic logic, we have proven infinity.
    I just hope that the information you acquire while walking along doesn't change your perception of it in the next round you go, which is why you don't see it as the same thing, but always as sth else.
    You always have finite infinitys, because an infinite infinity is equal to everything and nothing, which is a contradiction (unless it (consciousness) is just a spacetime distortion or rotational moebiusstrip twist drag, which defines dark energy/dark matter).
    Because infinitys are only describable in a set of certain parameters, they can only describe specific boundary-less sets within a set with boundaries, otherwise the complete opposite of any value always cancels out it's counterpart, which means that the the only solution is the empty set "{ }".
    It's better not to think about it. W8 but isn't it exactly that?

  • @Sultan-ni9ei
    @Sultan-ni9ei 6 років тому +4

    اللي عنده اختبار منطق وجاي يدور شرح يرفع يده 🙊

  • @fatimaroumeih651
    @fatimaroumeih651 4 роки тому

    Doctor what is the meaning of phi mean false ? Please answer me. I'm from Lebanon

  • @shafinibnemahmud1687
    @shafinibnemahmud1687 Рік тому +1

    My brain- What the fuck is this.

  • @md.yasinarafathpiyal2217
    @md.yasinarafathpiyal2217 3 роки тому

    Can anyone answer what typing tool he uses? thanks

  • @II_xD_II
    @II_xD_II 4 роки тому

    can i get some high school questions which uses contraposition and cases to prove itself ??

  • @zhen3356
    @zhen3356 8 років тому

    Thanks!

  • @williampercyzvenyika9441
    @williampercyzvenyika9441 7 років тому

    thank you sir

  • @dxnes5067
    @dxnes5067 4 роки тому +6

    lol I'm going to fail tomorrows exam

    • @MonsieurGilbert
      @MonsieurGilbert 4 роки тому +1

      Good luck, and report back brother.

    • @dxnes5067
      @dxnes5067 4 роки тому +3

      Ricardo Skylstad didn’t go as bad as I thought lol

    • @MonsieurGilbert
      @MonsieurGilbert 4 роки тому

      @@dxnes5067 Thats great to hear!

  • @ziliestarrive
    @ziliestarrive 6 років тому

    thank you!

  • @aqsayounus6236
    @aqsayounus6236 4 роки тому

    With someone with a horrible math intuition how can I tell if something has to be proved directly or by using contrapositive and contradiction? :(

  • @uzairakram899
    @uzairakram899 5 років тому

    So you show that a/b are not in lowest terms by showing that they are even. So how does that contradict the assumption that sqrt2 is rational(i.e sqrt2 can be expressed as ratio).

    • @uzairakram899
      @uzairakram899 5 років тому

      @Zachary Madden That definition seems like shooting an arrow and then drawing a circle around it.
      Ratios can be expressed in higher terms with common factors. There is no contradiction when you find a common factor in a ratio.

    • @uzairakram899
      @uzairakram899 5 років тому

      @Zachary Madden I understand with that contorted definition this would be a contradiction, I'm not arguing against the contradiction itself but against the definition that frames this as a contradiction.

    • @uzairakram899
      @uzairakram899 5 років тому

      @Zachary Madden Any number that can be written as a ratio.

    • @uzairakram899
      @uzairakram899 5 років тому

      pi is irrational so really there is no ratio that expresses pi.
      However, pi can still be written in an algebraic form pi=Circumafrance/diameter. But this doesn't actually mean that pi is rational, it can just be a ratio of two irrational numbers or at least the circumference is irrational.

    • @azizahmed7915
      @azizahmed7915 5 років тому

      @@uzairakram899 a rational number can be expressed in ratio a/b with a and b as integers. Whereas in the case with pi, one or the other must be irrational, so it does not fit in rational numbers definition

  • @joshanetomado8964
    @joshanetomado8964 9 років тому +6

    i just wanna ask.. where did u get "k"? ps: i'm still 13, still in 8th grade and our lesson is now like this..😱😱

    • @Trevtutor
      @Trevtutor  9 років тому +4

      +Joshane Tomado We can write any even number as 2k (where k is a variable and can be any integer). So I just picked k in this instance. I could have called it 2j, 2l, 2x, or anything, but it's just meant to show that the outcome is even.

    • @meliemmanuel7680
      @meliemmanuel7680 7 років тому +10

      13 and doing this!! am 23 and am beginning

    • @bestpcgaming7454
      @bestpcgaming7454 6 років тому +2

      13 and doing discrete... What are you? A Japanese?? An Indian??

    • @aileeroleda653
      @aileeroleda653 5 років тому

      I have a similar problem oof

  • @elangz9201
    @elangz9201 8 років тому

    why does it have to be on the lowest term? please answer :(

    • @Trevtutor
      @Trevtutor  8 років тому +8

      Definition of rational numbers.

  • @caiozowyecamachocabral5413
    @caiozowyecamachocabral5413 8 років тому +5

    I didn't understand WHY did you assume that the root(2) = a/b where a, b is in lowest terms! Why lowest terms?
    A rational number doesn't need to be a irredutible fration.....!

    • @Trevtutor
      @Trevtutor  8 років тому +4

      +Caio Zowye Camacho Cabral We assume lowest terms for contradiction. Basically, we want to say "here's an irreducible rational number that sqrt(2) is equivalent to", and then we come around and say "wait, this irreducible number just happens to be reducible. It can't be both, so this number can't be rational."

    • @rkcst6503
      @rkcst6503 7 років тому +1

      I also do not understand why the reducibility has anything to do with the rationality. Even after his answer, I don't know what the link is.

    • @rkcst6503
      @rkcst6503 7 років тому

      I don't get it. Can't I say that root 2 = a/b where be is a flying zebra and then say "wait, a/b is actually a number"
      Thats how it looks in my head. What am I missing?

    • @skylarkenneth2407
      @skylarkenneth2407 7 років тому

      Rational numbers: p/q (or a/b in this case) of two integers, and q (or b) is not 0 (whole number or irreducible fraction). Now, in TrevTutor's example, we come to find out that this "irreducible fraction" of a/b (where a is even and b is not 0 nor even or reducible in terms of the fraction because it is already in lowest terms; i.e. 2/1, 2/3, 2/5, 4/1, 4/3, etc) can be reduced once more, because now b is even (i.e. 2/2, 2/4, 2/6, 4/2, 4/6, etc). Thus concluding a contradiction that sqrt(2) is not rational... hope that helps

    • @danielwilson1606
      @danielwilson1606 7 років тому

      Honestly, a/b is assumed to be in lowest terms because the author of the video, who is a straight up boss btw, knew where the problem was going... If a/b wasn't assumed to be in lowest terms, I don't believe a contradiction could be drawn out.
      However, if a/b is assumed to be in lowest terms, as ALL rational numbers have a representation in lowest terms this is a fine assumption to make, then we know from the outside that both a and b CANNOT be even because if both were even then you could divide both by two, meaning a/b is not in lowest terms.

  • @mogencheng3829
    @mogencheng3829 7 років тому

    bless ur soul

  • @dubeya01
    @dubeya01 7 років тому

    How do we prove that proof by contradiction is a valid method of proof?

  • @sadaf243
    @sadaf243 5 років тому

    what does it mean to be in lowest terms

    • @wsk5nwytscnkfsu
      @wsk5nwytscnkfsu 5 років тому +1

      Shawn s it means a fraction which can’t be further reduced, meaning a and b does not share any common divisor (common factor) other than 1.

    • @sadaf243
      @sadaf243 5 років тому

      @@wsk5nwytscnkfsu thanks buddy

  • @sayafujimoto8199
    @sayafujimoto8199 8 років тому +1

    thanks! great help ^___^

  • @dkwroot
    @dkwroot 8 років тому

    Our professor solved sqrt(2) a little differently. He said that at the point 2b^2 = a^2 we can say that 2b^2 has an odd number of prime factors (2,b,b) and a^2 has an even number of prime factors (a,a). Then because each has a different number of prime factors, we can say that this is a contradiction. This relies on some knowledge of number theory, though.

    • @Trevtutor
      @Trevtutor  8 років тому

      Yeah, there are many proofs of this which will depend on which class/approach you're taking. There are many other problems you'll see consistently in your math courses that have different proofs depending on the approach/background knowledge.

  • @brandomiranda6703
    @brandomiranda6703 6 років тому

    How do u show that then not not phi is true?

  • @MeTube3
    @MeTube3 4 роки тому

    "because A squared is equal to two times some other number, we know that A squared is even". In isolation this is not a useful statement, because a student can think of of 3, 5 or 7 squared etc. It needs to be qualified by linking it to the other side of the equality. Held me up for a while figuring that out through some other videos.

    • @erzo9005
      @erzo9005 3 роки тому +1

      I got stuck on this. Can you explain? I don't understand what he means two times X number means a squared is even

    • @abab1247
      @abab1247 2 роки тому

      @@erzo9005 well what he meant was that since:
      2b^2 = a^2
      theyre the same thing since theyre both set equal to each other
      lets say we plug in 3 (an odd number) for b
      2b^2 = 2(3^2) = 2(9) = 18
      18 is an even number
      and this is true for any odd number we plug in for (b), and since a^2 is set equal to all this,
      we can safely say that a^2 is also even.

  • @jaswinderkaur6215
    @jaswinderkaur6215 6 років тому

    how we can prove p then q by contradiction

  • @MuneebNoor-i7c
    @MuneebNoor-i7c Рік тому

    luv u ...................

  • @helperbg4570
    @helperbg4570 3 роки тому

    What if tht was a decimal after being divided by 2

  • @poongothairagunathan1105
    @poongothairagunathan1105 2 роки тому

    where did the 2k squared come from

  • @Starkeweg
    @Starkeweg 2 роки тому +1

    I’m dropping out

  • @juannunez3224
    @juannunez3224 4 роки тому

    I hate the day I signed to this class

  • @camilledelavega5663
    @camilledelavega5663 3 роки тому

    Hello BSCS 1B.

  • @cosmickitty9533
    @cosmickitty9533 8 років тому

    what does bar mean?

  • @AcTommyX
    @AcTommyX 8 років тому

    That is a psi symbol not a phi

  • @robertshparuta7483
    @robertshparuta7483 2 роки тому

    good proof but the 2ksquared should be better explained for me it just fellout of the sky

  • @fikretcihan1747
    @fikretcihan1747 Рік тому

    Congratulations.
    Notification: I would like to inform you that I plan to include this video among the videos reviewed in my article "Analysis of UA-camTM Videos and Video Comments on Mathematical Proof Methods". Kind regards.

  • @zic6677
    @zic6677 9 місяців тому

    hey future students watching this...
    1.yeah proofs is impossible so goodluck
    2. no your not ever gonna use this in real life.
    3. good luck on your exam tomorrow :) (don't leave it last minute next time.)

    • @rockstarstudio2
      @rockstarstudio2 2 місяці тому

      @zic6677 Yh, you're right. I failed it three times already 🙃

  • @shinwarikhan4677
    @shinwarikhan4677 7 років тому

    Sir how we prove that" the sum of any rational and irrational number is irrational?

  • @rockstarstudio2
    @rockstarstudio2 2 місяці тому

    Yep
    I'm failing 😅

  • @Zooptopus27
    @Zooptopus27 6 років тому +2

    Great video, but I just want to take the time to say that this side of mathematics is complete rubbish! Ha

    • @strangerdanger7616
      @strangerdanger7616 4 роки тому

      Not really, without this you wouldn't have any other side of mathematics its like saying you like hate sperm but love babies, I know stupid example, but makes no sense it just sounds stupid.

    • @sunnyzhu5791
      @sunnyzhu5791 4 роки тому

      @@strangerdanger7616 your words is smart

  • @BenedictOtengRamarukuru
    @BenedictOtengRamarukuru 3 місяці тому

    😈😈💯

  • @morbidreality4909
    @morbidreality4909 2 роки тому

    I am really dumb