# Ideas for checking answers involving dy/dx or similar

**URL:** <https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246>\
**Category:** Questions\
**Tags:** simplefunction, patterns\
**Created:** [December 18, 2020, 7:41pm UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246 "2020-12-18T19:41:15Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Steve\_Rinard](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/steve_rinard/32/1799_2.png) [@Steve\_Rinard](https://cl.desmos.com/u/Steve_Rinard)\
**Post date:** [December 18, 2020, 7:41pm UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/1 "2020-12-18T19:41:15Z")

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I’m looking for ways that I might be able to check student answers that involve multiple variables and items like “dy/dx” or “dr/dt”, etc.

I usually use simpleFunction to check answers but that doesn’t work with variables like “dy/dx”.

Currently, the only way I can think of is to check their raw latex. That’s generally messy as there are too many possibilities for an answer.

For example, I want a student to find the derivative V=pi_r^3 or V=\frac{4}{3}\pi r^{3} with respect to t, so the student input to check would be dV/dt=4pi_r^2 \*dr/dt or \frac{dV}{dt}=4\pi r^{2}\cdot\frac{dr}{dt}.

Any other ideas besides checking raw latex of the input?

Parse equation?

Graphs?

Thanks!

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**Author:** ![Daniel\_Grubbs](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_grubbs/32/719_2.png) [@Daniel\_Grubbs](https://cl.desmos.com/u/Daniel_Grubbs)\
**Post date:** [December 18, 2020, 7:49pm UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/2 "2020-12-18T19:49:20Z")

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You can treat dy/dx as though it is a function of three variables, d, x and y, and evaluate that way.

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<div class="post-metadata">

**Author:** ![Steve\_Rinard](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/steve_rinard/32/1799_2.png) [@Steve\_Rinard](https://cl.desmos.com/u/Steve_Rinard)\
**Post date:** [December 18, 2020, 8:19pm UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/3 "2020-12-18T20:19:10Z")

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I’ve never thought of that!

That is a great solution as I can just set the values I’m not checking equal to “1”. Thanks Daniel!

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**Author:** ![Bryn](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/bryn/32/40_2.png) [@Bryn](https://cl.desmos.com/u/Bryn)\
**Post date:** [December 20, 2020, 9:01am UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/4 "2020-12-20T09:01:08Z")

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Except that they could just type y/x and get the same result?

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<div class="post-metadata">

**Author:** ![Daniel\_Grubbs](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/daniel_grubbs/32/719_2.png) [@Daniel\_Grubbs](https://cl.desmos.com/u/Daniel_Grubbs)\
**Post date:** [December 21, 2020, 7:51am UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/5 "2020-12-21T07:51:22Z")

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You could check if evaluating at d=0 is undefined.

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<div class="post-metadata">

**Author:** ![Steve\_Rinard](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/steve_rinard/32/1799_2.png) [@Steve\_Rinard](https://cl.desmos.com/u/Steve_Rinard)\
**Post date:** [November 17, 2023, 10:15pm UTC](https://cl.desmos.com/t/ideas-for-checking-answers-involving-dy-dx-or-similar/2246/6 "2023-11-17T22:15:48Z")

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This is really old but just in case someone ever searches, I’ve now been using the pattern matching components with good results for items like this!