Results 1 to 3 of 3

Math Help - Negative Base in a Logarithm

  1. #1
    Newbie
    Joined
    Oct 2008
    Posts
    23

    Negative Base in a Logarithm

    My text asks me to describe why it is I cannot put a negative base into a logarithm, and I can't figure why. I can see how it would cause problems, what with -2^3 won't give you a positive eight....? I don't get it. It seems to me that it could work out sometimes, but the text clearly states, "You cannot have a negative base". Thats all it says though. I reckon it assumes I should know, or it should be blatantly obvious, but I don't get it. Any thoughts?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member Twig's Avatar
    Joined
    Mar 2008
    From
    Gothenburg
    Posts
    396

    Hi

    I am really not sure either, but letīs say you take a negative number like -2, and raise it to 1/2. The square root of negative numbers isnīt definied for real numbers.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2008
    Posts
    4
    I think it is because a logarithm is a inverse function of f(x) = a^x, where x can be any real number. But a cannot be anything. If a = -2 then it is not a proper function, you've got something that "jumps", and if x = 1/2
    (-2)^(1/2) is not defined. so f(x) = a^x is defined

    So we've got a function f(x) that always has positive outcome, the inverse function therefore has to start with a positive (base) number.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Base Conversion - Negative Base
    Posted in the Number Theory Forum
    Replies: 7
    Last Post: August 3rd 2010, 05:13 AM
  2. Replies: 2
    Last Post: April 24th 2010, 07:38 PM
  3. Negative Base with a Power
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 17th 2009, 09:12 AM
  4. integrate logarithm with base 10
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 13th 2009, 05:01 PM
  5. exponential base. logarithm.
    Posted in the Algebra Forum
    Replies: 2
    Last Post: November 30th 2008, 08:15 PM

Search Tags


/mathhelpforum @mathhelpforum