What is f''(x) in terms of dx/dy?

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  • Опубліковано 17 лис 2024

КОМЕНТАРІ • 102

  • @blackpenredpen
    @blackpenredpen  4 місяці тому +5

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  • @mizarimomochi4378
    @mizarimomochi4378 4 місяці тому +29

    Why stop there? If you keep going via induction, you get the subfactorial to show up.
    f^(n)(x) = (-1)^(n + 1) * n!! * (d^2x/dy^2)/(dx/dy)^(2n - 1)

  • @TNT9182-j1e
    @TNT9182-j1e 4 місяці тому +138

    This is why it’s important to remember that dy/dx is not a fraction.

    • @sepdronseptadron
      @sepdronseptadron 4 місяці тому +25

      You can treat it like a fraction though
      just remember the dx in the bottom is a single variable, and can't be split into d and x

    • @gachanimestudios8348
      @gachanimestudios8348 4 місяці тому +4

      ​@sepdronseptadron tbh how I would say is that dy/dx is a quotient. But yeah that's true.

    • @caniraso
      @caniraso 4 місяці тому +11

      dy/dx=d(y)*(1/dx) it is fraction now

    • @fifiwoof1969
      @fifiwoof1969 4 місяці тому +3

      ​@@caniraso *PEN WHACK*

    • @johnleandrepermison7175
      @johnleandrepermison7175 4 місяці тому

      Thank You, now I know hahaha

  • @BleuSquid
    @BleuSquid 4 місяці тому +5

    Can you do a follow-up explaining why you didn't simplify further by cancelling a (dx/dy)/(dx/dy) out of the answer to get (d/dy)/(dx/dy)^2? It's been 20 years since I actively practiced calculus, so I'm a bit forgetful, but I love watching your vids!

  • @jackkalver4644
    @jackkalver4644 4 місяці тому +9

    d^2y/dx^2 is not a fraction. To be accurate, it really means d(dy/dx)/dx, which IS a fraction.

  • @belindedireds
    @belindedireds 4 місяці тому +49

    at 6:42 I think you have forgotten that dx/dy was risen to the 3td power, and you collected a 2nd power ;-)

    • @tymoteuszlewicki3267
      @tymoteuszlewicki3267 4 місяці тому +3

      And i thing, by his voice at the end, that this answer did not match his previous answer, but he kept going

    • @niom9446
      @niom9446 4 місяці тому +8

      6:42?

    • @NonTwinBrothers
      @NonTwinBrothers 4 місяці тому +2

      ​@@niom9446
      Uh oh, I think he edited it out of the video 😳

    • @niom9446
      @niom9446 4 місяці тому +2

      @@NonTwinBrothers oh…

    • @blackpenredpen
      @blackpenredpen  4 місяці тому +17

      Thanks for pointing that out! I just trimmed that part of the video out to avoid further confusion.

  • @perost1227
    @perost1227 4 місяці тому +32

    Missed one dx/dy in the numerator

  • @Matthew_Klepadlo
    @Matthew_Klepadlo 4 місяці тому +9

    Hey guys! Don’t be a third derivative!
    (Distance is the 0th derivative, velocity is the 1st, acceleration is the 2nd, …)

  • @0xymfzzty0
    @0xymfzzty0 4 місяці тому +5

    It’s a good day when bprp uploads

  • @This_is_Tadj
    @This_is_Tadj 4 місяці тому +4

    I think there's a mistake when u took the common factor (dx/dy) it'll be [(-d³x/dy³)(dx/dy)+3(d²x/dy²)²]/(dx/dy)⁵ at 6:42

  • @kicorse
    @kicorse 4 місяці тому +2

    The first term in the final numerator, -d^3x/dy^3, should be -(dx/dy)(d^3x/dy^3). The mistake was in the line before factoring out d^2x/dy^2.
    A good way of spotting this sort of mistake at the end is checking for dimensional homogeneity. The second term in the numerator has dimensions of x^2/y^4, so the first term also needs to have these dimensions.

  • @humberkger
    @humberkger 4 місяці тому +1

    Missed a dx/dy on the num since you collected the (dx/dy)² from (dx/dy)³, making the first term on num should be (dx/dy)² [ (dx/dy)(-d³x/dy³) + 3(d²x/dy²)² ]

  • @tog4ax897
    @tog4ax897 4 місяці тому +19

    I would like to see sin(cos(x)) = cos(sin(x)) the solutions would probably be wild

    • @AadarshTiwary-en2hy
      @AadarshTiwary-en2hy 4 місяці тому +2

      No bro there is no solution of this problem

    • @xinpingdonohoe3978
      @xinpingdonohoe3978 4 місяці тому

      @@AadarshTiwary-en2hy of course there are. Just check WolframAlpha for four different solution sets. They may be complex, but they certainly exist.

    • @bruhifysbackup
      @bruhifysbackup 4 місяці тому +3

      @@AadarshTiwary-en2hy hes probably asking about complex solns

    • @nanamacapagal8342
      @nanamacapagal8342 4 місяці тому +6

      i checked wolfram, the solutions are complex and WILD, but they are closed.
      not sure about sinh(cosh(z)) = cosh(sinh(z))...

    • @TOG3AX
      @TOG3AX 4 місяці тому +2

      yo i wanna see this too!

  • @danielnevesdepaiva
    @danielnevesdepaiva 4 місяці тому +1

    In the moment of the evidence of (dx/dy)², in the penultimate line, you missed one dx/dy, that must be multiplied by -d³y/dy³, in the numerator.

  • @epicurieux4161
    @epicurieux4161 4 місяці тому +1

    Could you please do the integral from 0 to inf of (arctan(x))^2/x^2 and then from 0 to 1? 😊

    • @sachavalette1437
      @sachavalette1437 4 місяці тому +1

      Fan de Axel Arno ?? 😏

    • @epicurieux4161
      @epicurieux4161 4 місяці тому

      @@sachavalette1437 yep 😂 j'avais envie de voir si il allait approcher le problème d'une autre manière

  • @xinpingdonohoe3978
    @xinpingdonohoe3978 4 місяці тому +2

    Isn't it possible that d³y/dx³ could be 1/(dx³/d³y) simply because dx³/d³y may not have been defined to be anything else yet (to my knowledge), so we can make it as such?
    I guess it depends on what the operator 1/d could suggest. d and ∫ are inverses. ∫dx=x, ∫dσ=σ, etc. Sure, they're multivalued functions, with infinitely many branches from all the constants we could add, but for simplicity we can focus on just one branch. So 1/d would undo 1/∫? There might have been a joke Dr. Peyam video using something like this, but I don't know of any too-rigourous maths that's used it.

  • @nicolasguguen5918
    @nicolasguguen5918 Місяць тому

    Technically, wouldn’t it be correct to say that d²y/dx²=1/(dx²/d²y) ?

  • @jimschneider799
    @jimschneider799 4 місяці тому

    @0:55 - Shouldn't that have been f'(x)*dx/dy, since you are taking derivatives with respect to y?

  • @geektoys370
    @geektoys370 4 місяці тому

    It is a fraction

  • @tse4620
    @tse4620 4 місяці тому

    So after trimming the video, is the final ans correct now?

  • @teaformulamaths
    @teaformulamaths 4 місяці тому

    Hey, are there any health implications for working around so much dried ink? Are there such things as healthy board pens?

    • @poteyatocheapp6978
      @poteyatocheapp6978 3 місяці тому

      yes, you'd become extremely susceptible to dried ink syndrome. Symptoms include being hypnotised to write math on and on and on

  • @محمدوحيد-ظ3ح
    @محمدوحيد-ظ3ح 4 місяці тому

    Can you translate the videos into Arabic, because I am an Arab and I love hearing you very much. I want you to ask a question: Is this a method of study? ❤❤❤❤❤❤❤❤

  • @v8torque932
    @v8torque932 4 місяці тому +2

    I can smell the dry erase marker through the screen

  • @jomariraphaellmangahas1991
    @jomariraphaellmangahas1991 2 місяці тому

    Now do the reverse and you get the solution for the differential equation

  • @MaherHamza-y5c
    @MaherHamza-y5c 2 місяці тому

    Give us some examples

  • @ParveshIITB
    @ParveshIITB 4 місяці тому

    glad that brilliant changed its font😅

  • @niom9446
    @niom9446 4 місяці тому

    t the end isnt it legal to flip the (dx/dy)^3 to the top to make it (dy/dx)^3?

    • @xninja2369
      @xninja2369 4 місяці тому

      Yeah , but remember only in (dx/dy)³ not in dx³/d³y ..
      Also I think it's just how this is normally taught in high school I guess..
      It's easier to remember..

    • @niom9446
      @niom9446 4 місяці тому

      @@xninja2369 hm ok

  • @Keerthidayarathna
    @Keerthidayarathna 4 місяці тому

    One can understand this by 2nd order differentials

  • @tychovanbrabant5279
    @tychovanbrabant5279 4 місяці тому

    What is the differens between d/dy and dx/dy?

    • @APaleDot
      @APaleDot 4 місяці тому

      "d/dy" is an is an operator which takes a function of y to its derivative.
      "dx/dy" is the derivative of x with respect to y.

    • @tychovanbrabant5279
      @tychovanbrabant5279 4 місяці тому

      @@APaleDot d/dy is when you have to take derivative, dx/dy is the derivative?

    • @APaleDot
      @APaleDot 4 місяці тому

      @@tychovanbrabant5279
      dx/dy is a derivative, yes.
      d/dy turns a function into its derivative.

  • @gajananjoshi1313
    @gajananjoshi1313 4 місяці тому

    From indai 🇮🇳

  • @ValidatingUsername
    @ValidatingUsername 4 місяці тому

    People just need to stop using d$variable1/d$variable2 where it’s not denoting an incomplete derivative or the exact f’($variable2)

  • @billycheung5114
    @billycheung5114 4 місяці тому

    Inspiring 😮

  • @APaleDot
    @APaleDot 4 місяці тому

    But the real question here is what is d²x/dy²?

  • @_BlackNoir_
    @_BlackNoir_ 4 місяці тому +4

    He purposely made the mistake in second last line to rage bait interaction in comments

  • @arise.2196
    @arise.2196 4 місяці тому +1

    if 0.9999.... is 1 ( since there is no real number between them ) then is [0.999...] =1?
    or
    is 1 > 0.9999... by dx which will result in [0.999...] = 0
    i am confused🙏

    • @theweirdwolf1877
      @theweirdwolf1877 4 місяці тому

      Yeah I was also confused about that
      My maths teacher said it was 0 though

    • @xninja2369
      @xninja2369 4 місяці тому

      ​​@@theweirdwolf1877Technically 0.999..... is another way of defining 1 , like how you define 1/3= 0.3...
      It's because there's is no real number bigger than 0.99999.. but less than 1 , suppose if you stop at 0.9999999 it's finite number not infinite 0.999....
      You can also prove it this way
      1) X=0.999...
      2)10x=9.99..
      2)-1)
      10x-x=0.99..-0.999 ...
      9x=9
      X=1
      This is correct algebraic method..
      There is also other methods as well..
      So [0.999...] should be one... .
      I don't care about your math teacher , search up this on Google if you don't believe..

    • @bruhifysbackup
      @bruhifysbackup 4 місяці тому

      dx is not a value, it IS an infinitesimally small amount

    • @theweirdwolf1877
      @theweirdwolf1877 4 місяці тому

      @@bruhifysbackup the point is that 0.9999… is less than 1 by an infinitesimally small amount, that is, dx

    • @aravindhvijayanandan3010
      @aravindhvijayanandan3010 4 місяці тому

      ​@@bruhifysbackupdx definitely is a value with an infinitesimal order of magnitude. It is very, very small.

  • @Kotuseid
    @Kotuseid 4 місяці тому +1

    🗿

  • @Vikrampratapmaurya
    @Vikrampratapmaurya 4 місяці тому

    Second last step is wrong?? 😊 when u r taking (dx/dy)^2 as common then bracket must hv first term -dx/dy.d^3x/dy^3

  • @slooth-pn6gn
    @slooth-pn6gn 4 місяці тому

    anze yu

  • @atzuras
    @atzuras 4 місяці тому +1

    Abuse of notation