# How to check correct with a logarithmic equation (not base 10)

**URL:** <https://cl.desmos.com/t/how-to-check-correct-with-a-logarithmic-equation-not-base-10/947>\
**Category:** Questions\
**Tags:** validation, correctness\
**Created:** [May 2, 2020, 5:43pm UTC](https://cl.desmos.com/t/how-to-check-correct-with-a-logarithmic-equation-not-base-10/947 "2020-05-02T17:43:59Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![hannah.mcdowell](https://avatars.discourse-cdn.com/v4/letter/h/838e76/32.png) [@hannah.mcdowell](https://cl.desmos.com/u/hannah.mcdowell)\
**Post date:** [May 2, 2020, 5:43pm UTC](https://cl.desmos.com/t/how-to-check-correct-with-a-logarithmic-equation-not-base-10/947/1 "2020-05-02T17:43:59Z")

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Hi - I am trying to have students rewrite exponential equations as logarithmic equations. I would love it to self-check.

I tried converting the student response to latex and using that in my correct sink, but it doesn’t work. Not sure what to try next.

Here is a link to the slide:  
[Logs and Exponents Troubleshooting](https://teacher.desmos.com/activitybuilder/custom/5eadb0724a5a060c8dd35ede)

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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:** [May 2, 2020, 11:03pm UTC](https://cl.desmos.com/t/how-to-check-correct-with-a-logarithmic-equation-not-base-10/947/2 "2020-05-02T23:03:43Z")

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It’s really, really difficult to match latex, but this works:

`isCorrect = numericValue(parseEquation(this.latex).rhs) = numericValue(parseEquation(this.latex).lhs) and countNumberUsage(this.latex,2)=1 and countNumberUsage(this.latex,32)=1 and countNumberUsage(this.latex,5)=1`

I’d also add this line in, so it doesn’t show the calculation (and then undefined once an = is inserted):  
`disableEvaluation: true`

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<div class="post-metadata">

**Author:** ![hannah.mcdowell](https://avatars.discourse-cdn.com/v4/letter/h/838e76/32.png) [@hannah.mcdowell](https://cl.desmos.com/u/hannah.mcdowell)\
**Post date:** [May 3, 2020, 7:15pm UTC](https://cl.desmos.com/t/how-to-check-correct-with-a-logarithmic-equation-not-base-10/947/3 "2020-05-03T19:15:42Z")

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Thank you so much! I really appreciate it - worked like a charm!