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A Tough One From the American Maths Olympiad








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Today a fun one from the 2021 ‘Murican IMO 🙂 We need to find the sum of all real, positive solutions of x^2^sqrt(2)=sqrt(2)^2^x . Some boundary restrictions and function analysis gets the job done quite elegantly 🙂 =D Enjoy! =)

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30 Comentários

  1. _That was quite some fun, don't you agree? 🙂 Check deez out to support the channel btw <3 _
    Train your Calculus Expertise by trying out Brilliant! =D https://brilliant.org/FlammableMaths

    Check out my newest video over on @Flammy's Wood ! =D https://youtu.be/bRCV9ZaTeeY

    Support the channel by checking out Deez Nutz over on https://stemerch.eu/products/deez-nuts-premium-3d-cutting-board?_pos=1&_sid=3ebd4ef06&_ss=r ! :3

    Engi Watch: https://stemerch.com/products/the-incredibly-unrigorous-engineering-watch?variant=40377075728562

  2. would it be acceptable to just use trial and error to figure out the values of S? Or would it be a given that you have to use calculus

  3. i don't know why i haven't been able to place your accent, when you spoke German i felt like more of an idiot than when trying to understand half of the maths
    other half helps though don't worry

  4. Hello teacher, how are you? I have a question for you, please answer. What books do you recommend for me to prepare for the Mathematical Olympiads? Thanks in advance! ❤️😔

  5. Always the weird noises in the beginning of the video that i look forward everyday

  6. I love your videos Flammy, but tbh this should not qualify as a hard problem as my two guess solutions would immediately give me the answer

  7. This is not an olympiad question (olympiads are harder). This problem is from a math contest called the AMC12, specifically the 2021 AMC12B (Part B test/exam) Problem 21. This is pre-olympiad level in the US, along with AIME.

  8. I don’t understand 80% of the stuff you do but the 20% i understand is insanely valuable to me. Thank you ❤️

  9. As S is the SUM of all +ve values of x between √2 – 4, shouldn't the answer b S<6 (as there's 2,3 etc between em), or am i missing something. It's bothering me 🥲

  10. No log needed
    say f = x^2^sqrt(2) and g = sqrt (2)^2^x
    Sqrt(2) solves by inspection
    f is less than g @ x=0, overtakes g @ sqrt (2) (check by seeing f'>g' @ x =sqrt(2)) but must be overtaken by g at some point bc g is growing exponentially and f is a polynomial.
    Try x = 4, see that f<g, so already overtaken
    So I1=sqrt(2) & sqrt (2)<I2<4 2sqrt(2)<S<4+sqrt(2), which corresponds to sqrt(2)<S<6, or C
    Don't know how to prove these are the only intersections tho

  11. Whoa YouTube decided to just block your channel notifs for some reason and didnt realise you posted so many vids 😐

    also nice biceps

  12. Can someone esplain me the shirt joke? Is it an obvious one and I'm just dumb hahaha?

    Edit I gonna try to think it out lol brb…

    Ohhh, I remember my physics teacher telling us those terms, and apparently the next are snap ,crackle and pop… idk if he was lying to make me look like and idiot tho… oh wikipedia agrees about the rice crispies mascots

  13. x^a = b^x | log( … )

    a * log(x) = x * log(b)

    log(x)/x = log(b)/a

    Substitute: α = – log(b)/a, y = 1/x

    y log(1/y) = -α | * (-1)

    y log(y) = α

    Substitute: y = e^z, z = log(y)

    z * e^z = α | W( … )

    z = W(α)

    Resubstitute and use property of Lambert function:

    y = e^z = e^(W(σ)) = α/W(α)

    Resubstitute:

    x = 1/y = W(α)/α

    —————–

    EDIT: Oops, I had read the task wrong.

    x^a = b^(c^x) | log( … )

    a * log(x) = c^x * log(b) | Log( … )

    Log(a) + Log(log(x)) = x * Log(c) + Log(log(b))

    Log(log(x)) = x * Log(c) + Log(log(b)) – Log(a)

    Define:

    f(x) = Log(log(x))

    g(x) = Log(c) * x + Log(log(b)) – Log(a)

    Zero Point of g(x):

    x0 = -(Log(log(b)) – Log(a))/Log(c)

    Choose:

    log( … ) = log[b]( … )

    Log( … ) = log[c]( … )

    Therefore:

    g(x) = x – Log(a)

    x0 = Log(a)

    Use condition: a = c^b

    g(x) = x – b

    x0 = b

    Consider: x = b^n

    F(n) = f(b^n) = Log(log(b^n)) = Log(n)

    G(n) = g(b^n) = b^n – b

    Find n, such that F(n) = G(n). We get:

    n = 1: F(1) = Log(1) = 0, G(1) = b – b = 0

    First solution: x1 = b.

    For n = c^k, we get:

    F(c^k) = Log(c^k) = k

    G(c) = b^(c^k) – b = R

    If R > k, then b^(c^k) is upper boundary:

    b^(c^k) – b > k <=> c^k > log(k + b)

    With b = sqrt(2) and c = 2, we get with k = 2:

    sqrt(2)^4 – sqrt(2) = 4 – sqrt(2) ≈ 2.68.. > 2

    Therefore b^(c^k) = 4 is upper boundary.

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