The number e explained in depth for (smart) dummies



In this follow-up video to his “e to the i pi for dummies” video the Mathologer sets out to properly explain the coolest features of the famous number e and the exponential function e^x. Find out WHY e is irrational, how you go about calculating the first 1,000,000 digits of e, WHY the exponential function e^x is its own derivative, etc.

Here are links to the videos that I refer to in this video:

e to the pi i for dummies: (this is the video I summarise at the beginning)

Indeterminate: the hidden power of 0 divided by 0: (about derivatives, among other things)

Math in the Simpsons: e to the i pi: (this is the video that I refer to at the very end)

This week’s t-shirt I made myself. Check out this wiki page about this pretty identity

Thank you very much to my friend Marty Ross for proofwatching drafts of this video and helping me to get the words “just right” and to Danil Dmitriev the official Mathologer translator for Russian for his subtitles.

Enjoy!

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32 Comments

  1. 178482301^(1/19) is sick close to e. There seems to be an integer sequence {1, 3, 8, 19, …} (I lack the computing power and/or know-how to go further) such that e to this power is closer to an integer than any lower value (3, 20, 2981, and the aforementioned 178482301). (I've excluded 0 for obvious reasons.) Haven't checked OEIS. But this means that 3^1, 20^(1/3), 2981^(1/8) and 178482301^(1/19) make closer and closer approximations to e, and these are the local minimum error cases.

  2. 8:40 I think you mean: ”The error, we get, by chopping off, at the Nth term, is LESS, THAN 1/N!.”; seeing, as we arrived at 1/N!, by simplifying the bracketed expression; which, in this case, made the bracketed expression bigger; and, indeed, the expression:
    ”error < 1/N!”, on screen, is correct. 🤔

  3. I never understood logarithms before but now at least I have an inkling about how they are used. It seems to me that smaller and smaller measurements of slope between points on a graph function is the basis of calculating the derivative. Why not just say that the derivative is the exact value of that slope?

  4. The Euler identity comes from the Euler formula which is obviously wrong because one side is the exp function ranging to infinity but the other side is finite (sum of 2 trig functions each ranging from -1 to 1). So, both Euler 's inventions are wrong.

  5. I enjoyed the explanation….it's very clear without looking complicated….I recall the quote from Einstein that if you can't explain it simply, you don't understand it well enough….you did it…thank you…

  6. hey so what's (∞/∞!)? could we define that as an approximate ratio, for practical computation purposes? if you call it zero then that'd basically contradict the small-angle approximation method, right?

  7. 7:47 If you instead replace all the factors in the denominators with 8, then the error would be less than 1/(7×7!)=0.0000283447… which is a much closer upper bound of the true error which in this case would be 0.0000278602…

    I wonder how much closer you can get to the true error while still "simplifying" the right hand side to a small-ish closed form expression in terms of N, where N is the number of terms you take from the series, i.e. in this case N=8.

  8. Another great video from mathologer! Except for one part (at least for me), which is the proof, that e must be irrational: Just slightly change 19/7 to 18/7, and the unequality holds (18/7 minus the chunk in the brackets is a fraction less than 1/7!). It's easy to see, that this is true for a/b in general, as long as there are no further restrictions to the integers a and b, and as long as we are not talking about the absolute value of the result (Mathologer did not).
    Am I wrong? If yes, I'd appreciate a short explanation, why. In that case, pls. keep it 'simple & stupid', because I'm not a mathematician, and English is not my first language…

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