Need slider to go backwards once

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

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.

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