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Re: Log[4]==2*Log[2]


Andreas,

In my view two symbolic expressions are not necessarily equal if
numerically they are equal.

What you wish to know is if the left and right hand sides can be
brought to a standard form and then if the standard forms are equal.
To achieve this you may wright:

(Log[4] // Simplify) == (2*Log[2] // Simplify)

that gives a solid True.


Regards
Peter





Andreas Stahel <sha at hta-bi.bfh.ch> wrote in message news:<chp8q9$jjm$1 at smc.vnet.net>...
> To whom it may concern
> 
> the following answer of Mathematica 5.0 puzzeled me
> 
> Log[4]==2*Log[2]
> leads to
> 
> N::meprec: Internal precision limit $MaxExtraPrecision = 50.` reached while \
> evaluating -2\Log[2]+Log[4]
> 
> with the inputs given as answer. But the input
> 
> Log[4.0]==2*Log[2]
> 
> leads to a sound "True"
> 
> Simplify[Log[4]-2*Log[2]]
> leads to the correct 0, but
> Simplify[Log[4]-2*Log[2]==0]
> yields no result
> 
> There must be some systematic behind thid surprising behaviour.
> Could somebody give me a hint please
> 
> With best regards
> 
> Andreas


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