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

• To: mathgroup at smc.vnet.net
• Subject: [mg50635] Re: Log[4]==2*Log[2]
• From: p-valko at tamu.edu (Peter Valko)
• Date: Wed, 15 Sep 2004 01:49:34 -0400 (EDT)
• References: <chp8q9\$jjm\$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```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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