The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

No Logarithm of a Negative Number

Date: 8/6/96 at 21:22:36
From: Anonymous
Subject: Logarithm of Negative Number


Please tell me how to solve this problem:

log(-5) = ?

Date: 8/6/96 at 21:47:11
From: Doctor Robert
Subject: Re: Logarithm of Negative Number

Since a logarithm is an exponent, your question is equivalent to the 
question "What power of 10 gives me -5?"  

Positive exponents of 10 do not give negative results, and neither do 
negative exponents.  The answer is that you cannot find the logarithm 
of a negative number (at least, not over the set of real numbers).

I hope that this helps.

-Doctor Robert,  The Math Forum
 Check out our web site!   
Associated Topics:
High School Logs

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.