thanks for the great limit!

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  • Опубліковано 16 січ 2024
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КОМЕНТАРІ • 61

  • @huguesbornet1211
    @huguesbornet1211 5 місяців тому +34

    Loved the comment on the margin “Fermat could not use” ( for his unknown demonstration so far; unless a piece of paper from back then once pops up)

  • @winky32174
    @winky32174 5 місяців тому +10

    I love when difficult limits simplify so nicely!

  • @pietropellegrini7926
    @pietropellegrini7926 5 місяців тому +25

    I don't know of you remember but you have already done a video on this problem... It was question B5 in the 2004 Putnam

    • @MichaelPennMath
      @MichaelPennMath  5 місяців тому +28

      I realized this after recording, but I decided to post since someone emailed the suggestion in.

    • @gp-ht7ug
      @gp-ht7ug 5 місяців тому +2

      Me too i noticed it had already been published but I always like this limit

    • @gp-ht7ug
      @gp-ht7ug 5 місяців тому +2

      Me too i noticed it had already been published but I always like this limit

  • @krisbrandenberger544
    @krisbrandenberger544 5 місяців тому +6

    @ 14:14 The numerator should have x^m, not x^(m+1).

    • @Hiltok
      @Hiltok 5 місяців тому

      Good spot.

  • @neilgerace355
    @neilgerace355 5 місяців тому +1

    3:42 😆

  • @whonyx6680
    @whonyx6680 5 місяців тому +5

    You could have just used the taylor series of the logarithm, no point in transforming it into an integral.

    • @divisix024
      @divisix024 5 місяців тому +1

      To top it off, the way he did it is basically just deriving the Taylor series of the logarithm

  • @CamEron-nj5qy
    @CamEron-nj5qy 5 місяців тому +1

    Lowercase Pi in the thumbnail had me confused for a second

  • @selimakar7201
    @selimakar7201 5 місяців тому

    Good job Mr Penn

  • @iithomepatnamanojsir
    @iithomepatnamanojsir 5 місяців тому +1

    Very nice sir

  • @user-br1sl4us4e
    @user-br1sl4us4e 5 місяців тому +6

    Hi prof, I was reading this article An Elementary Proof of the Strong Law of Large Numbers by N. Etemadi, but had troubles to understand from eq 6 on. I was wondering if you could make a video on it!

  • @chrayma
    @chrayma 5 місяців тому

    So beautiful !!

  • @Xv8M4g3r
    @Xv8M4g3r 3 місяці тому

    Why does this not end up a L=1 by substituting x=1 into the original formula? x^z for x=1 is just 1 regardless of z. So everything inside of the infinite product just cancels to 1 (no longer depending on n). The product of an infinite number of 1s is just 1 so L=1. I've obviously missed something, but I can't see what?

  • @goodplacetostop2973
    @goodplacetostop2973 5 місяців тому +3

    16:42

  • @markmajkowski9545
    @markmajkowski9545 5 місяців тому +2

    The x~1- ^n to infinity seems to require something more formal since 1^N = 1

    • @Hiltok
      @Hiltok 5 місяців тому +3

      There is a difference between
      limit as n goes to infinity of ( limit as x approaches 1 from below of x )^n = ( 1 )^n = 1
      and
      limit as n goes to infinity of ( limit as x approaches 1 from below of of (x^n) ) = 0.
      Any instance of x is strictly less than 1 despite the limit being equal to one.
      As the power goes to infinity, anything less than exact equality of x with 1 sees the result go to zero.

    • @markmajkowski9545
      @markmajkowski9545 5 місяців тому

      Seems to require more than an assertion - plus then this function would seem to have discontinuity at 1 or Lim approaches 1+ which seems of interest.

    • @user-jn9hs5ry7h
      @user-jn9hs5ry7h 5 місяців тому +2

      For any x1- , we get 0.

    • @Hiltok
      @Hiltok 5 місяців тому

      @@markmajkowski9545
      At x=1, the product collapses to just 1. i.e. product for n=0 to infinity of (2/2)^(1^n) = (1^1)^N as N goes to infinity = 1 since the base is now exactly 1.
      For x approaches 1 from above, the base is strictly >1 and the power (x^n) goes to infinity, so the total product blows up to infinity.

  • @emperorOfMustard
    @emperorOfMustard 5 місяців тому

    I knew that e would pop up just from the statement...

  • @trippia6865
    @trippia6865 5 місяців тому

    Right now I'm taking a multivariable calculus course in uni and i have a question about this sort of problems in general. How can I decide on what substitutions, change of variables or any changes on the product/sum/integral/limit that I have in a problem like the ones you solve in the channel in order to proceed? While you're solving the problems the changes are so clear and easy to understand because of the structure of the expression but when I'm faced with different problems I don't always know what I should do. Is there a better way to learn how I can think of these changes by myself? Some examples could be like when you integrate under the sum, the 0'th integral or contour integration. How could i determine which technique is the best for the problem other than when there's a very obvious solution?

  • @gabrielcampello7836
    @gabrielcampello7836 5 місяців тому

    great

  • @unknownstoneageman81
    @unknownstoneageman81 5 місяців тому

    🔥

  • @farfa2937
    @farfa2937 5 місяців тому

    Series being able to be doms and subs implies the existance of switch series

  • @user-kp1ci5jj8q
    @user-kp1ci5jj8q 5 місяців тому +1

    Professor,Can you talk about geometry problems? I am so weak in that Field, please:)

    • @bjornfeuerbacher5514
      @bjornfeuerbacher5514 5 місяців тому

      He already did lots of geometry problems in older videos, look around on his channel.

    • @user-kp1ci5jj8q
      @user-kp1ci5jj8q 5 місяців тому

      Thank you my brother

  • @asifkarim75
    @asifkarim75 5 місяців тому

    Your video always helps me to understand the physics and mathematics, thanks

  • @Noam_.Menashe
    @Noam_.Menashe 5 місяців тому +2

    I don't know why but this seems familiar.

    • @nirajmehta4264
      @nirajmehta4264 5 місяців тому +2

      i think he did this problem before, or a similar one.

  • @rafaelalcala6939
    @rafaelalcala6939 3 місяці тому

    Can someone explain better why does the series converge ar 14:38 ? Or a better explanation of whats happening hee?

  • @markmajkowski9545
    @markmajkowski9545 5 місяців тому

    That’s what he said - but I seems to warrant a more extensive proof than the assertion since x less than 1 - raising to infinite power gives 0. That FEELS like an indeterminate form in need of another step or two as proof. If such out there maybe you know where to look. Thanks

    • @Cinnabar_Rhubarb
      @Cinnabar_Rhubarb 5 місяців тому +1

      There's no indeterminate form since, inside the N limit, x is not changing at all. If you had something like (1 + 1/n)^n, then the base is approaching 1 at the same time as the exponent is growing large, which leads to an indeterminate form. Here, x^n is saying "take a fixed base

  • @JRabba1995
    @JRabba1995 5 місяців тому +1

    Can someone explain why the infinite product cant be evaluated at x=1 and get a limit of 1? I guess it has to do with the continuity but it is not obvious to me why it is not continuous

    • @bjornfeuerbacher5514
      @bjornfeuerbacher5514 5 місяців тому

      If you evaluate it at x = 1, you get an infinite product 1 times 1 times 1 times ..., i. e. 1 to the power of infinity. And that's not defined.

    • @JRabba1995
      @JRabba1995 5 місяців тому

      @@bjornfeuerbacher5514 the exponentiation is performed inside the product and the exponent would also be 1 after evaluation

    • @aniruddhvasishta8334
      @aniruddhvasishta8334 5 місяців тому

      To add onto another reply, 1^infty is an indeterminate form that can take on different values depending on how the limit is approached. For a canonical example, note that lim n->infty (1+1/n)^n = e. Doing it the usual way you'd think that the part in parentheses goes to 1 and the exponent goes to infinity and you might think it's 1, but that's not how all limits work.

    • @JRabba1995
      @JRabba1995 5 місяців тому

      @@aniruddhvasishta8334 i would agree except that in this case the exponent does not tend to infty if x=1

    • @aniruddhvasishta8334
      @aniruddhvasishta8334 5 місяців тому

      @@JRabba1995 I'm not sure I understand. There is no x in my limit?

  • @Happy_Abe
    @Happy_Abe 5 місяців тому +3

    Can someone explain @15:40?

    • @ibaijurado279
      @ibaijurado279 5 місяців тому +1

      yeah pls

    • @idjles
      @idjles 5 місяців тому

      @@ibaijurado279he breaks it into A/m + B/(m+1) and ends up
      With well-known (1-1/2+1/3-1/4…=ln 2) (oscillating harmonic series) with some coefficients, and a change of index to get the 1.

    • @IoT_
      @IoT_ 5 місяців тому

      ​@@ibaijurado279you can use PFE
      \frac{(-1)^{m + 1}}{m(m + 1)} = \frac{-1}{m} + \frac{-1}{m + 1}
      And after use the Taylor series of ln(1+x) twice. That's it

    • @bjornfeuerbacher5514
      @bjornfeuerbacher5514 5 місяців тому

      Do you know how partial fraction decomposition works? If yes, that step is easily done; if no, it requires a longer explanation. ;)

    • @Happy_Abe
      @Happy_Abe 5 місяців тому

      @@bjornfeuerbacher5514 I do, but it’s a sum not an integral

  • @viggo2112
    @viggo2112 5 місяців тому

    Bros hairline has an infinite limit

  • @OlympiadProblemsolving
    @OlympiadProblemsolving 5 місяців тому

    ua-cam.com/video/EGHnkT8WoSA/v-deo.html