# Correctness of a draggable point

**URL:** <https://cl.desmos.com/t/correctness-of-a-draggable-point/647>\
**Category:** Questions\
**Tags:** validation, correctness\
**Created:** [December 15, 2019, 11:03pm UTC](https://cl.desmos.com/t/correctness-of-a-draggable-point/647 "2019-12-15T23:03:04Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Melissa\_Lute](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/melissa_lute/32/437_2.png) [@Melissa\_Lute](https://cl.desmos.com/u/Melissa_Lute)\
**Post date:** [December 15, 2019, 11:03pm UTC](https://cl.desmos.com/t/correctness-of-a-draggable-point/647/1 "2019-12-15T23:03:04Z")

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First of all, I am NEW at this! And I’m trying to learn how to make self-graded tests.

I have [this question](https://teacher.desmos.com/activitybuilder/custom/5df6ba2d14460c34d803a4f6) where I would like students to place a point on the graph at the solution to the system. I am now stuck. I have a draggable point and I have a correct function, but no matter where the point is dragged to, it gives the check mark. How do I fix this? Or is there a better way I could be doing this?

Thanks.

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**Author:** ![Werner\_Pries](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/werner_pries/32/129_2.png) [@Werner\_Pries](https://cl.desmos.com/u/Werner_Pries)\
**Post date:** [December 16, 2019, 11:42am UTC](https://cl.desmos.com/t/correctness-of-a-draggable-point/647/2 "2019-12-16T11:42:41Z")

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A couple of things:

1. You probably should put a “step” on the values of a1 and b1 to make it easier to get an exact answer. Some suitable value (such as 0.5)
2. You might also want to add the label of the point so a student can see how “exact” their answer is.
3. Your “correctness” did not take into account the student’s coordinate point.

Take a look at this reworked solution:

> **[\[Copy of\] Draggable point • Activity Builder by Desmos](https://teacher.desmos.com/activitybuilder/custom/5df76ab6105a680182562a6c)**
>
> by Werner Pries

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**Author:** ![Melissa\_Lute](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/melissa_lute/32/437_2.png) [@Melissa\_Lute](https://cl.desmos.com/u/Melissa_Lute)\
**Post date:** [December 16, 2019, 1:17pm UTC](https://cl.desmos.com/t/correctness-of-a-draggable-point/647/3 "2019-12-16T13:17:39Z")

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Thank you so much! I thought there was something I was missing.