# [LON-CAPA-users] Formula response won't recognize "pi"

H. K. Ng hkng at fsu.edu
Thu Nov 21 14:11:42 EST 2019

Hi,

Formularesponse using  cas with maxima works great.

<problem>
<script type="loncapa/perl">
$ansa = &cas('maxima','1/sqrt(4*pi^2*L*C)'); </script> <startouttext />What is formula for resonant frequency for an LC circuit? <endouttext /><br /> <startouttext /><m>$ \omega_{res} = $</m><endouttext /> <formularesponse answer="$ansa" id="12">
</formularesponse>

</problem>

Regards,
-hk

On Thu, Nov 21, 2019 at 11:05 AM SIMIN, GRIGORY <SIMIN at engr.sc.edu<mailto:SIMIN at engr.sc.edu>> wrote:

Hi all!

I've found a strange issue in some problems requiring formula response.

I have a simple question to enter the formula for the resonant frequency.

An example of correct answer is (in other variations the formula could be a bit more complex than this one)

1/(2*pi*sqrt(L*C))

The correct solution is checked by sampling L and C values.

When I am entering the answer, I can see that LON-CAPA recognizes it because it displays the formatted formula as I am entering it:

[cid:16e8f5cf6cc6917eb1]

But when I press submit, I got the response:

“unable to understand formula”

By experimenting with this, I found that the issue happens because of “pi” being a part of the answer.

If pi is replaced with 3.141, everything would work.

But it feels weird asking students to enter 3.141 instead of pi; besides, I don’t even want to give them a hint that pi is a part of the answer.

Why is this happening? Apparently LON-CAPA knows what “pi” means because it displays it correctly.

Thanks!

Grigory

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