I use the definiton and build around the definition, not everyone does gesture this way. I feel like it works better for me.
Absolute Value:
"Absolute value (hold hand vertically and parallel to each other) is the distance (spread your arms far apart) from a number (on one hand hold up all 5 fingers andstart moving that hand towards the other) to zero (use the other hand to make zero)"
I will have to think about the other two... they have very wordy definitons that involve other complex concepts - are you already using a gesture for variable? (I use - pulling on a mask, since a variable is like a disguise) What about for constant or coefficent, if you already have gestures for those we can use those gestures to create a concept gesture for algebraic expression.