# [LON-CAPA-users] Extracting the numerical value from a solve() Maxima command

Gerd Kortemeyer korte at lite.msu.edu
Fri Jan 27 19:41:19 EST 2012

```Hi,

Could you please send me the XML source code for your problem?

Thanks,

- Gerd.

On Jan 27, 2012, at 6:14 PM, Seema Ali wrote:

> Hi,
>
> This was my attempt to get Maxima to solve the following equation:
> \$base1^\$power1maxima = \$base2^\$power2maxima
> where \$power1maxima and \$power2maxima are linear equations and
> \$base1 and \$base2 are constant values.
>
> Below is a snippet of part of my code:
>
> \$solution = &cas('maxima',"float(solve((\$power1maxima)*log(\$base1) = (\$power2maxima)*log(\$base2),x))");
> \$solution =~ /(-?\d+(?:\.\d+)?)/;
>
>
> Here are a couple of examples of some values:
>
> Example 1:
> An equation it is trying to solve: (2 * x)*log(7) = (-7 * x - 7)*log(9)
> \$solution is [x = -.7980624185332027]
>
> Example 2:
> An equation it is trying to solve: (2x)log(4)=(?5x?8)log(3)
> \$solution is [x=?1063303930517583]
>
> The answer for Example 2 should be -1.063303930517583.  If I double click on the values on the page I get the decimal point, otherwise if I highlight them which is what I did for Example 2, the decimal is missing, which is a separate issue.
>
> Example 2 also generates this error:
> ERROR: Computer's answer is incorrect ("-1.063303930517583"). It is likely that the tolerance range [-1.06340393051758, -1.06320393051758] needs to be adjusted.
> This error occurred while processing response 1_7 in part 0
>
> My tolerance range is 5%.
>
> I think it is my attempt at a regular expression is probably causing this problem.
>
> How do I extract the numerical value from a solve command in Maxima?
>
>
> Thanks.
>
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```