• calcopiritus@lemmy.world
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    1 month ago

    This triangle is impossible.

    If the distance between B and C is 0, B and C are the same points. If that is the case, the distances between A and B and A and C must be the same.

    However, i ≠ 1.

    If you want it to be real (hehe) the triangle should be like this:

        C
        | \
    |i| |  \ 0
        |   \
        A---B
         |1|
    

    Drawing that on mobile was a pain.

    As the other guy said, you cannot have imaginary distances.

    Also, you can only use Pythagoras with triangles that have a 90° angle. Nothing in the meme says that there’s a 90° angle. As I see it, there are only 0° and 180° angles.

    Goodbye, I have to attend other memes to ruin.

    • thomasloven@lemmy.world
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      1 month ago

      Context matters. In geometry i is a perfectly cromulent name for a real valued variable.

    • planish@sh.itjust.works
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      1 month ago

      This is clearly meant to be a right triangle. And the distances between the points are the same (because the squares of the coordinate differences are the same), just the directions are different.

      If you move 1 unit forward, turn the correct 90 degrees, and then move i units forward, you will end up back where you started.

      • calcopiritus@lemmy.world
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        1 month ago

        You can’t have a distance in a “different direction”. That’s what the |x| is for, which is the modulus. If you rotate a triangle, the length of the sides don’t change.

        • planish@sh.itjust.works
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          1 month ago

          The vector from one point to another in space has both a distance (magnitude) and a direction. Labeling the side with i only really makes sense if you say we’re looking at a vector of “i units that way”, and not at an assertion that these two points are a directionless i units apart. Then you’d have to break out the complex norms somebody mentioned.

  • manucode@infosec.pub
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    1 month ago

    1 • 1 + i • i = 1 + (-1) = 0 = 0 • 0

    Pythagoras holds, provided there’s a 90° angle at A.

    • Foofighter@discuss.tchncs.de
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      1 month ago

      But that’s not the definition of the absolut value, I.e. “distance” in complex numbers. That would be sqrt((1+i)(1-i)) = sqrt(2) Also the triangle inequality is also defined in complex numbers. This meme is advanced 4-4*2=0 Works only if you’re doing it wrong.

  • xylogx@lemmy.world
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    1 month ago

    In the complex plane each of these vectors have magnitude 1 and the distance between them is square root of two as you would expect. In the real plane the imaginary part has a magnitude of zero and this is not a triangle but a line. No laws are broken here.

    • DragonTypeWyvern@midwest.social
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      1 month ago

      Literally, this is one of those questions where they’re testing logic and your understanding that the figures aren’t necessarily representative of physical reality.

  • i_love_FFT@jlai.lu
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    1 month ago

    I kept seeing this pop up recently, and I finally understand it: it’s an introductory problem in Lorentzian general relativity.

    AB is a space-like line, while AC is a time-like line. Typically, we would write AC as having distance of 1, but with a metric such that squaring it would produce a negative result. However it’s similar to multiplying i to the value.

    BC has a distance of 0, but a better way of naming this line would be that it has a null interval, meaning that light would travel following this line and experience no distance nor time going by.

    I’m sure PBS Spacetime would explain all of this better than me. I just woke up and can’t bother searching for the correct words on my phone.

  • technocrit@lemmy.dbzer0.com
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    1 month ago

    Maybe the problem is constructing a metric that makes this diagram true. Something like d(x,y) = | |x| - |y| | might work but I’m too lazy to check triangle inequality.

    • stevedice@sh.itjust.works
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      1 month ago

      Triangle inequality for your metric follows directly from the triangle inequality for the Euclidean metric. However, you don’t need a metric for the Pythagorean Theorem, you need an inner product and, by definition, an inner product doesn’t allow non-real values.

  • OrganicMustard@lemmy.world
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    1 month ago

    You can make something like this properly by defining a different metric. For example with metric dl2 = dx2 - dy2 the vector (1, 1) has length 0, so you can make a “triangle” with sides of lengths 1, -1 and 0.

    • Kogasa@programming.dev
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      1 month ago

      That’s not a metric. In any metric, distances are positive between distinct points and 0 between equal points

      • OrganicMustard@lemmy.world
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        1 month ago

        It depends which metric definition are you using. The one I wrote is a pseudo-Riemannian metric that is not positive defined.

        Normally physicists use that generalized metric definition because spacetime in most cases has a metric signature of (-1, 1, 1, 1). Points with zero distance are not necessarily the same point, they just are in the same null geodesic.

        • Kogasa@programming.dev
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          1 month ago

          You’re talking about a metric tensor on a pseudo-Riemannian manifold, I’m talking about a metric space. A metric in the sense of a metric space takes nonnegative real values. If you relax the condition that distinct points have nonzero distance, it’s a pseudometric.

  • deikoepfiges_dreirad@lemmy.zip
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    1 month ago

    funny Interpretation: in the complex plane, the imaginary axis is orthogonal to the real axis. so instead of the edge marked with i (AC), imagine an edge of length 1 orthogonal to that edge. It would be identical to AB, so AC CB is 0.