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Example meaningful function that is product of two other functions

  1. May 28, 2009 #1
    What could be a real-life example (so no imaginary units and stuff :approve:) where the product of two elimentary functions of one random variable has a meaningful interpretation.

    Let's say I have a function that maps my random monthy income to number of days I can live off it and another function maps the same random monthly income to taxes owned on this income. Like:
    Days I can live off (income) = income / 20 :cool:
    Taxes owned on (income) = income * 0.34 :yuck:

    However their product, taxes times days, has no meaning at all. :confused:

    So could someone help me? :shy:
  2. jcsd
  3. May 28, 2009 #2
    Imaginary units are plenty useful in real life (ie physics)

    Anything that you can multiply together and which can vary can have a real life meaning

    m(t) = mass of an object at time t (You can think of some reason why the mass would change, eg maybe its a meteor
    a(t) = accelaration at time t (meteor getting closer to a planet?)

    (ma)(t) = Weight of meteor at time t
  4. May 29, 2009 #3


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    Area of a rectangle in which the lengths of the sides are changing with time was the first thing that came to my mind.
  5. May 29, 2009 #4

    matt grime

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    Why does it have no meaning at all? Just because you can't think of an obvious one doesn't mean that it's useless.
  6. May 29, 2009 #5

    Perhaps I should substitute "meaning" by "useful in average Joe's everyday life".

    Like for example, the value of the function of variable x that gives us the prevailing interest rate multiplied by the value of the function of variable x that gives us the starting capital of average Joe. Their product would be the interest payment that Joe could receive. I just can't think of variable x that both affects Joe's starting capital and interest rates.
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