I can use y = 1/100x as a linear transition between x:0, y:0 and x100, y1

I'm trying to understand how to create a "curved" transition thats "easing in" and "easing out" in a symmetrical fashion?
The function y = x^2 is curved but its not symmetrical within x:0, y:0 and x100, y1
How can I create "symmetrically" curved transitions in the style of the ones below?

Ideally the function would contain a variable that controls the amount of curve, (from curved the one way to a straight line and then to curved again the other way). Please excuse my lack of vocabulary and understanding in the field, I hope the question makes sense. Thanks

