# Need slider to go backwards once

**URL:** <https://cl.desmos.com/t/need-slider-to-go-backwards-once/1122>\
**Category:** Questions\
**Created:** [June 12, 2020, 5:03pm UTC](https://cl.desmos.com/t/need-slider-to-go-backwards-once/1122 "2020-06-12T17:03:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Katie\_Artzt](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/katie_artzt/32/839_2.png) [@Katie\_Artzt](https://cl.desmos.com/u/Katie_Artzt)\
**Post date:** [June 12, 2020, 5:03pm UTC](https://cl.desmos.com/t/need-slider-to-go-backwards-once/1122/1 "2020-06-12T17:03:54Z")

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I am trying to do coterminal angles on the unit circle. I have an angle between 0-2pi and have a second terminal side rotate showing a coterminal angle. I am using the once forward option. So when the student presses play it rotates and stops showing the angle is coterminal.

There does not seem to be an option for a slider to go backwards once. Does someone have a work around?

I am trying to to make it happen on slide 3 of my activity builder.  
[Reference and CoTerminal Angles](https://teacher.desmos.com/activitybuilder/custom/5ee13aba3257c42d52413a37)

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**Author:** ![cwinske](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/cwinske/32/3106_2.png) [@cwinske](https://cl.desmos.com/u/cwinske)\
**Post date:** [June 12, 2020, 6:02pm UTC](https://cl.desmos.com/t/need-slider-to-go-backwards-once/1122/2 "2020-06-12T18:02:38Z")

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If I’m understanding correctly, you would like the animation to go in reverse of what is shown in slide 2? If so, this should work. I created a new variable, c, that calculates the values that you want. I also changed all the b variables to c in the other expressions. All the CL can remain the same.

> **[\[Copy of\] Reference Angles and Co-Terminal Angles • Activity Builder by Desmos](https://teacher.desmos.com/activitybuilder/custom/5ee3be826f46246001b8fbf9)**
>
> Help from Activity Builders Created by
> Luke Walsh

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<div class="post-metadata">

**Author:** ![Katie\_Artzt](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/katie_artzt/32/839_2.png) [@Katie\_Artzt](https://cl.desmos.com/u/Katie_Artzt)\
**Post date:** [June 12, 2020, 6:33pm UTC](https://cl.desmos.com/t/need-slider-to-go-backwards-once/1122/3 "2020-06-12T18:33:50Z")

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No this is not what I am looking for. In slide 2, the coterminal angle goes around 2pi+the angle and stops. So the student can see that it “starts” at the x-axis and rotates to the same location.

I need a slider (or a way to make a slider happen) where it rotates from the x-axis backwards. While I typed this I figured it out. I need to change the function not the slider. I have my backwards rotating terminal side angle now. thanks for your input