A Viewer Suggested Equation | Problem 293

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  • เผยแพร่เมื่อ 14 ต.ค. 2024
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ความคิดเห็น • 26

  • @ejvalpey
    @ejvalpey 3 หลายเดือนก่อน +3

    I really wish you had plotted the solutions for us.

    • @XJWill1
      @XJWill1 3 หลายเดือนก่อน +1

      See my other comment for the equations you can plot to visualize the infinite number of solutions.

  • @hafizusamabhutta
    @hafizusamabhutta 2 หลายเดือนก่อน

    Which app do you use?

    • @aplusbi
      @aplusbi  2 หลายเดือนก่อน

      Notability

  • @XJWill1
    @XJWill1 3 หลายเดือนก่อน +2

    To visualize in the complex plane the infinite number of complex z values that solve the equation,
    exp( Log(z) / z ) = i
    plot the following sets of curves and observe the intersection points
    0 = x * ln(x^2 + y^2) + 2*y * atan2(y , x)
    1 = tan( (1/2 *x*atan2(y , x) - 1/4 *y*ln(x^2 + y^2) ) / (x^2 + y^2) )
    If using Desmos, note that atan2(y , x) is entered as arctan(y , x)

    • @XJWill1
      @XJWill1 3 หลายเดือนก่อน +2

      The curves become difficult to resolve as you zoom in, like fractals. Desmos sometimes creates artifacts in the graphs, but if you keep zooming in you can get better resolution.
      One thing that is interesting to see from the graph, that I think is difficult to realize if the solution is given in terms of the product-log function, is that there is only 1 solution with negative real part (real part is approximately - 1.86). Any of the other infinite number of solutions have positive real part.

  • @Skyler827
    @Skyler827 3 หลายเดือนก่อน +3

    I tried it and got a very different wrong answer.... 😅 but still, great problem and great solution!

    • @aplusbi
      @aplusbi  3 หลายเดือนก่อน

      Thanks!

  • @scottleung9587
    @scottleung9587 3 หลายเดือนก่อน

    Cool!

  • @Nobodyman181
    @Nobodyman181 3 หลายเดือนก่อน

    U are fun❤😄

    • @aplusbi
      @aplusbi  3 หลายเดือนก่อน +1

      u is funner than me 😜

  • @mcwulf25
    @mcwulf25 3 หลายเดือนก่อน +2

    Not as straightforward as it first appears. I rearranged to get
    u = 1/z
    u^u = -i
    Which didn't simplify!

    • @aplusbi
      @aplusbi  3 หลายเดือนก่อน

      A nice way to approach it, though

    • @XJWill1
      @XJWill1 3 หลายเดือนก่อน +1

      @mcwulf25
      It appears that you assumed (1/u)^u = 1 / u^u
      I wonder if you proved that to be the case. Because in general
      (1 / w)^p is not equal to 1 / w^p
      For example, w = - 1 and p = 1/2 demonstrates the inequality of the more general case
      For (1/u)^u and 1 / u^u , try u = - 1/2

    • @rishy773
      @rishy773 3 หลายเดือนก่อน +2

      It does actually simplify!! There is this super cool function called the "super square root," which is defined such that ssrt(x) is the inverse of x^x (it can also be calculated through ssrt(x) = e^(W(lnx)).) Therefore, you can say:
      u^u = -i
      u = ssrt( -i )
      1/z = ssrt( -i )
      z = 1/(ssrt( -i ))
      = 1/ (e^(W(ln(-i))))
      = e^-(W(-i*pi/2)) (which is the same as the the answer he gave! - it is just the 'principal value' or where n = 0)
      ≈ 0.438 + 0.361i

  • @XJWill1
    @XJWill1 3 หลายเดือนก่อน +2

    Your mistake is equating ln( z ^ (-1) ) = -1 * ln(z)
    That is not true in general. It is only an identity for real z > 0
    For other values of z, equality does not always hold

    • @xleph2525
      @xleph2525 3 หลายเดือนก่อน

      Can you point out a particular value of z which does not hold for ln( z ^ (-1) ) = -ln(z)?

    • @XJWill1
      @XJWill1 3 หลายเดือนก่อน +1

      @@xleph2525 The most obvious failure is - 1

    • @82rah
      @82rah 3 หลายเดือนก่อน +1

      How is the problem solved without making this mistake?

    • @xleph2525
      @xleph2525 3 หลายเดือนก่อน

      @@XJWill1 I see your point, but nothing like -1 was being operated on in the string of reasoning. In fact, it is very apparent that no real z < 0 can be a solution. I suppose there could have been a disclaimer in the video with that observation, but I don't believe that would have been necessary.
      On a side note, I think -ln(z) = ln( z^-1 ) does hold true for z = a + bi. I encourage you to try a few complex numbers and see what happens.

    • @XJWill1
      @XJWill1 3 หลายเดือนก่อน +1

      @@xleph2525 You obviously do not understand identities and real and complex numbers.

  • @alexandermorozov2248
    @alexandermorozov2248 3 หลายเดือนก่อน

    Ну и чему же равно z?

  • @stevemonkey6666
    @stevemonkey6666 3 หลายเดือนก่อน

    Okay, but I actually do prefer tea. 😅

    • @aplusbi
      @aplusbi  3 หลายเดือนก่อน

      Absolutely: |Tea| 😁