Complex numbers - help needed

Discussion in 'OT (OFF Topic) Forums' started by markjay, Oct 25, 2016.

  1. markjay

    markjay MB Master

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    Anyone.....?

    [​IMG]

    I am struggling to help my daughter with material I studied half a century ago.... :(
     
  2. Tim203

    Tim203 Active Member

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    I'll ask someone tomorrow for you.
     
  3. OP
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    markjay

    markjay MB Master

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    Thanks!
     
  4. GLK

    GLK MB Enthusiast

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    Tried to type in here, but can't make the superscript, so a screenshot:

    [​IMG]

    ... I think ... it's been 35 years at least :dk:


    PS Sorry, should've included the formula: (a+bi)(c+di) = (ac−bd) + (ad+bc)i
     
    Last edited: Oct 25, 2016
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    markjay

    markjay MB Master

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    Thanks GLK! This looks correct (to my untrained eye). Will check with her tomorrow....
     
  6. MercedesDriver

    MercedesDriver MB Enthusiast

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    And now this brings to mind Moivres theorem and I can't sleep.
     
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  7. Druk

    Druk MB Enthusiast

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    I'm usually struggling with my Tesco bill. What application would this stuff have in the real world? Serious question.
     
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    markjay

    markjay MB Master

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    I get brownie points with little Miss MJ?
     
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  9. GLK

    GLK MB Enthusiast

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    No idea ...

    I didn't even remember at first what complex numbers were, or what imaginary number is, for that matter (was it always called that?).

    It took a few minutes to recall, and I was told that, at my age, I should always welcome a chance to exercise little grey cells :wallbash:
     
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  10. Palfrem

    Palfrem MB Enthusiast

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    The only imaginary number I can bring to mind is the number of glasses of vin rouge I tell my wife I enjoyed before bed.
     
  11. GLK

    GLK MB Enthusiast

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    So, basically you go to bed with a bunch of square roots of minus one :thumb:


    PS My wife and I enjoy our wine together, so I don't get a chance to employ higher maths there :dk:
     
  12. GordonTarling

    GordonTarling MB Enthusiast

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    Other than allowing you to pass exams, I guess it might come in handy if you're a rocket scientist. :)
     
  13. grober

    grober MB Master

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  15. Tim203

    Tim203 Active Member

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    Apparently you need to know the rules for imaginary number: i x i = -1 square root of -1 = i 15 is correct as GLK said. My work colleague and GLK are clever, that's all I can add to it. Right over my head!
     
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  16. Ted

    Ted MB Enthusiast

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    Last edited: May 19, 2017
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    markjay

    markjay MB Master

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    She approves :thumb:
     
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  18. lisa110rry

    lisa110rry Active Member

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    I'm pretty hot with Excel/Access calculations but they are always centred around cost recovery on construction projects. I could not begin to understand the aforementioned!
     
  19. knighterrant

    knighterrant MB Enthusiast

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    First off, electrical engineers like me use "j" because "i" is almost always used to mean "current" in our equations. Where most people would write "a + bi", we'd write "a + bj", but it means the same thing.
    Electrical engineers often have to solve "differential equations" (remember them), which are a bit hard to explain without delving into calculus. Basically, a differential equation relates functions to their rates of growth. The solution to a differential equation is usually a function, not a number. As a specific example (keeping away from electrical engineering), suppose you have a snowplow that keeps piling up more and more snow in front of it so that the further it goes, the heavier the load it is pushing, and the heavier the load, the slower it goes, and the slower it goes the slower the pile of snow in front of it grows. You can (with a differential equation) relate the amount of snow at a given time t [call it A(t)] to the velocity of the plow, and the equations can be solved to give the function A(t) at all times t. But often, it's easier to solve differential equations in the domain of complex numbers because the equations are a lot nicer, but you know that the solution you care about is just the real part of the solution.
    Sorry, that was making sense as I wrote it, but now that I read it with an imaginary new hat on, it'a not great as an answer. So I'll just have to say that there are uses for complex numbers in some fields, just not those filled with potatoes for Tesco.
     
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  20. Steveml63

    Steveml63 MB Enthusiast

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    Hi,
    For me, one of the more complex real world maths applications must be in formula 1.
    The teams need to work out whether to send cars out on hard or soft tyres for different amounts of laps vs lap times vs pit stop times - plus factor in the reducing weight of the car as it burns fuel.
    It must have been even more complex when you could refuel and therefore have higher and lower weights during the race!
    Cheers
    Steve
     

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