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Are logarithms only non-negative?

  1. Aug 11, 2013 #1
    I read that logb x exists only when x >= 0

    what about log-3 -27 though?

    The answer should be the exponent 3, right?

  2. jcsd
  3. Aug 11, 2013 #2
    You can define the logarithm for all nonzero real numbers. But this requires complex number theory. So it's not suitable for high school.
  4. Aug 11, 2013 #3
    Thanks, I read the above though in the book Pre-Calculus for Dummies. It said all logarithms and bases were non-negative. I'm not that good on trigonometry or pre-calc.
  5. Aug 11, 2013 #4
    Yeah. So for now just take it as given that the bases are nonnegative. You might see the more general theory later.
  6. Aug 11, 2013 #5
    Thank you. I will take your advice. Any less work for me is a good thing!
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