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From: bs@linus.UUCP (Robert D. Silverman)
Newsgroups: net.lang.c
Subject: Re: Exponetiation
Message-ID: <174@linus.UUCP>
Date: Wed, 25-Jun-86 14:52:47 EDT
Article-I.D.: linus.174
Posted: Wed Jun 25 14:52:47 1986
Date-Received: Fri, 27-Jun-86 03:12:33 EDT
References: <366@bucsb.bu.edu.UUCP> <5664@alice.uUCp>
Organization: The MITRE Corporation, Bedford, MA
Lines: 12

> > I'm confused. I've been trying to figure out a quick and easy way
> > to exponetiate to a fraction (ie. x^(4.25))  and also be able to
> > figure out the power when given the base and the result.  
> 
> a^b is exp(b*ln(a)).  So, if x = a^b and you know a and x,
> 
> 	exp(b*ln(a)) = x
> 	b * ln(a) = ln(x)
> 	b = ln(x) / ln(a)

Better make sure that a,x > 0 before using this well known trick.
Bob Silverman