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Expanding log(a+b)

  1. Nov 2, 2005 #1
    anyoen know how to expand this? i can't think of any obvious way...
  2. jcsd
  3. Nov 2, 2005 #2


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    What kind of result are you looking for - functions of a and b separately? As it stands, it is as simple as possible.
  4. Nov 2, 2005 #3


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    There's not much you can do. In some cases, it's useful to factor it as [tex]\log a+\log(b+1)[/tex], but in general there's nothing simpler than the way you wrote it.
  5. Nov 2, 2005 #4
    i have a deceptively simple question you see:

    X^3 = (cY+d)^2

    where c and d are constants, with x and y the variables. how would you plot the 2 variables as a straight line graph. i'm having an idiocy attack and can only think "log it...."
  6. Nov 2, 2005 #5
    Take the log of Y and graph x, log y.
  7. Nov 2, 2005 #6
    that doesn't plot that relationship as a straight line though does it?

    i was under impression you had to transform [said equation] into a y=mx+c type form
  8. Nov 2, 2005 #7


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    You can't plot things like [itex]x^3=y^2[/itex] as a straight line on a normal graph.
  9. Nov 3, 2005 #8
    I didn't mean that would give you a formula, but if you had a set of data, you could find the regression by plotting x, log y. It's not the answer but it's a way to get it.
  10. Nov 4, 2005 #9


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    No, none of log-log, log-linear or linear-log will make that equation a straight line.

    What's the full context of the problem, do you have a number (more than 2) of x,y points and you wish to find constants c and d that give the "best fit" in some particular sense?
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