• shapis@lemmy.ml
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    2 days ago

    This very nice Romanian lady that taught me complex plane calculus made sure to emphasize that e^j*theta was just a notation.

    Then proceeded to just use it as if it was actually eulers number to the j arg. And I still don’t understand why and under what cases I can’t just assume it’s the actual thing.

    • jsomae@lemmy.ml
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      1 day ago

      e𝘪θ is not just notation. You can graph the entire function ex+𝘪θ across the whole complex domain and find that it matches up smoothly with both the version restricted to the real axis (ex) and the imaginary axis (e𝘪θ). The complete version is:

      ex+𝘪θ := ex(cos(θ) + 𝘪sin(θ))

      Various proofs of this can be found on wikipeda. Since these proofs just use basic calculus, this means we didn’t need to invent any new notation along the way.

      • shapis@lemmy.ml
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        22 hours ago

        I’m aware of that identity. There’s a good chance I misunderstood what she said about it being just a notation.

        • jsomae@lemmy.ml
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          17 hours ago

          It’s not simply notation, since you can prove the identity from base principles. An alien species would be able to discover this independently.

    • carmo55@lemmy.zip
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      1 day ago

      It is just a definition, but it’s the only definition of the complex exponential function which is well behaved and is equal to the real variable function on the real line.

      Also, every identity about analytical functions on the real line also holds for the respective complex function (excluding things that require ordering). They should have probably explained it.

      • shapis@lemmy.ml
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        1 day ago

        She did. She spent a whole class on about the fundamental theorem of algebra I believe? I was distracted though.

    • frezik@lemmy.blahaj.zone
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      2 days ago

      Let’s face it: Calculus notation is a mess. We have three different ways to notate a derivative, and they all suck.

      • JackbyDev@programming.dev
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        1 day ago

        Calculus was the only class I failed in college. It was one of those massive 200 student classes. The teacher had a thick accent and hand writing that was difficult to read. Also, I remember her using phrases like “iff” that at the time I thought was her misspelling something only to later realize it was short hand for “if and only if”, so I can’t imagine how many other things just blew over my head.

        I retook it in a much smaller class and had a much better time.