Solving An Interesting Log Equation | Math Olympiads

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  • Опубліковано 26 гру 2024

КОМЕНТАРІ • 53

  • @spelunkerd
    @spelunkerd Рік тому +10

    What I like about your videos is how you consistently do not choose the obvious pathway that most of us would use. In this case rather than following the blaring siren to change base, you chose more elegant pathways to get the same place. Just because they may take a little longer at times does not take away the theme that there are often many options. Along the way we recall principles that aren't necessarily used every day.

    • @SyberMath
      @SyberMath  Рік тому +4

      💖 Thank you for the feedback! My mindset seems to be "How can I make the solution more complicated?" It's funny that I haven't thought of the "change of base" method for this problem. Thanks for the heads up!!!

    • @leif1075
      @leif1075 Рік тому

      @@SyberMath Thank you for sharing. Wouldn't you agree your teo methods here are the same method thoigh just swapping bases?

    • @SyberMath
      @SyberMath  Рік тому

      @@leif1075 no problem! That’s right. They are kind of the same. Using change of base, which, interestingly I haven’t thought of btw, would be an entirely different approach.

    • @oahuhawaii2141
      @oahuhawaii2141 4 місяці тому

      @SyberMath: I did the change to a common base, and got a general form; then, I could choose base e, 2, 3, 10, ...
      log2(x) + log3(x) = 1, switch to a common base
      log(x)/log(2) + log(x)/log(3) = 1
      log(x)*(log(3) + log(2)) = log(2)*log(3)
      log(x) = log(2)*log(3)/log(6), choose base e
      x = e^[ln(2)*ln(3)/ln(6)] = e^(1/(1/ln(2) + 1/ln(3))) ≈ 1.5295923284918...
      BTW, with the exponent having a product and a quotient of logs, we can change bases for exponentiation and logarithm.
      Arranging for e^ln(2):
      x = e^[ln(2)*ln(3)/ln(6)]
      = [e^ln(2)]^[ln(3)/ln(6)] = 2^log6(3)
      This is the same if we chose base 2 instead of e.
      Arranging for e^ln(3):
      x = e^[ln(2)*ln(3)/ln(6)]
      = [e^ln(3)]^[ln(2)/ln(6)] = 3^log6(2)
      This is the same if we chose base 3 instead of e.

  • @justabunga1
    @justabunga1 Рік тому +28

    There is another method that you can also use, which is the change of base formula. This equation can be rewritten as log(x)/log(2)+log(x)/log(3)=1. Multiply everything by the LCD, which is log(2)log(3), and factor out log(x). This means that (log(3)+log(2))log(x)=log(2)log(3). Divide both sides by log(3)+log(2), or log(6). log(x)=log(2)log(3)/log(6), and x=10^(log(2)log(3)/log(6)). Simplify this even better and using properties of logarithms, which is x=2^(log_6(3)). The answer can also be x=3^(log_6(2)) if we interchange the the base of the exponent and the log of an argument.

    • @rajatdogra96
      @rajatdogra96 Рік тому

      Agreed same

    • @SyberMath
      @SyberMath  Рік тому

      Nice! 🤩

    • @MichaelRothwell1
      @MichaelRothwell1 Рік тому

      Agreed, that was my method (though I used ln rather than log). I was very surprised that SyberMath didn't present this method also, as the equation is crying out for the change of base rule!
      Also, this method leads to a pleasing symmetrical result, easily simplified to the forms found in the video.

    • @iz8376
      @iz8376 Рік тому

      yeah I did this method in my olympiad too and saves a lot of time

    • @ytlongbeach
      @ytlongbeach Рік тому

      yup. i did it the same way !!

  • @erikdahlen9140
    @erikdahlen9140 Рік тому +2

    I did log base change in my head when i saw the problem, factored, and solved for x. easier than whatever you did here

  • @broytingaravsol
    @broytingaravsol Рік тому +6

    x=2^(ln3/ln6)

  • @rajatdogra96
    @rajatdogra96 Рік тому +2

    Log x ( log 2 + log 3) = log 2 * log 3

  • @MushookieMan
    @MushookieMan Рік тому +6

    I just used the change of base formula on one of the logs, wasn't a bad method

  • @MarCamus
    @MarCamus Рік тому +1

    Changed both bases to ln
    and after some algebra I got the solution in terms of ln and e

  • @christianlopez1148
    @christianlopez1148 9 місяців тому +1

    log2x=lnx/ln2, log3x=lnx/ln3....easyly you can find lnx.

  • @somnathkundu7354
    @somnathkundu7354 Рік тому +1

    Do the change of base and add the terms.

  • @KookyPiranha
    @KookyPiranha Рік тому

    Aint no way this is a math olympiad problem. I saw a similar one in my hw

  • @giuseppemalaguti435
    @giuseppemalaguti435 Рік тому

    x=3^log6(2)

  • @tetsuyaikeda4319
    @tetsuyaikeda4319 Рік тому +1

    I could know 'Zee is not see, nor c, nor be ' that must be some kind of joking

  • @scottleung9587
    @scottleung9587 Рік тому

    I got the same answer the first method had.

  • @moeberry8226
    @moeberry8226 Рік тому +6

    The fastest way is to use change of bases. So you obtain log(x)/2+log(x)/3. Now just factor out a log(x) and divide by that constant on both sides and then anti log both sides and your done.

    • @SyberMath
      @SyberMath  Рік тому

      Nice! 🤩

    • @royfeer8651
      @royfeer8651 Рік тому +1

      smart way!

    • @oahuhawaii2141
      @oahuhawaii2141 4 місяці тому

      Not correct. The 2 should be log(2), and the 3 should be log(3). The base of the log can be chosen as 2, 3, e, 10, ...

    • @moeberry8226
      @moeberry8226 4 місяці тому

      @@oahuhawaii2141 your 100 percent right bro. That’s a typo on my end.

  • @rakenzarnsworld2
    @rakenzarnsworld2 Рік тому

    x = 1.5

  • @Education-35
    @Education-35 8 місяців тому +1

    My answer is same but another approach
    First i use reciprocal property
    To make same base
    And then take LCM
    And apply log(a) + log(b) = log(ab)
    After that
    Use base changing property
    And I got answer 2
    JEE aspirant
    2025
    🔥🔥🔥

    • @SyberMath
      @SyberMath  Місяць тому +1

      Best of luck! 😍😍

    • @Education-35
      @Education-35 Місяць тому +1

      @@SyberMath
      very few months left for success
      🔥🔥🔥

  • @josemanuelbarrenadevalenci653

    Confusedly explained

  • @GurpreetSingh-PI
    @GurpreetSingh-PI 9 місяців тому

    ELEGANT - spy x family

  • @GreenMeansGOF
    @GreenMeansGOF Рік тому

    change of base is how I would have done it

  • @MrGeorge1896
    @MrGeorge1896 7 місяців тому

    I suggest using ln(b) / ln(a) instead of log_a(b).
    ln(x) (1 / ln(2) +1 / ln(3)) = 1
    ln(x) = ln(2) * ln(3) / ln(6)
    so x = e ^ (ln(2) * ln(3) / ln(6)) = 1.52959...

  • @phongvong8639
    @phongvong8639 Рік тому

    It is over I mean they are. Then something has to be prioritised. Please. Thank you.

  • @popitripodi573
    @popitripodi573 Рік тому

    I used the change of base method!!your approach was very good alternative!!!!❤❤❤❤

  • @jfcrow1
    @jfcrow1 Рік тому

    x equal cube root of 3

  • @gatosimple2354
    @gatosimple2354 Рік тому

    Profe menos palabras demás,sea más directo

  • @MichaelRothwell1
    @MichaelRothwell1 Рік тому

    In case anyone is wondering, the reason for the rule
    a^(log꜀b)=b^(log꜀a)
    is that if you log each side to base c and use the power rule for logs, both sides give log꜀a log꜀b.
    Putting it another way,
    c^(log꜀a log꜀b)=(c^log꜀a)^log꜀b=a^log꜀b
    and
    c^(log꜀b log꜀a)=(c^log꜀b)^log꜀a=b^log꜀a
    so a^(log꜀b)=b^(log꜀a).

  • @Burningarrow7
    @Burningarrow7 Місяць тому

    You over complicated it wayyyy too much. I feel sorry for your students

    • @CriticSimon
      @CriticSimon Місяць тому

      Feel sorry for yourself, dude! 😂

  • @angelamusiema
    @angelamusiema Рік тому

    x=2-1