An Arc with all moving points!

I need to get an arc between two points ...

The Points A and B can be adjusted with sliders for the coordinates ...

Another slider is t ... The red Point is called B° ...

How do I get an arc between B and B°? 

This arc should open in the same way as the direction in which point B° moves ... 

So the arc should give the path of the moving point B° ...

A is the Center ...

Points A and B can be adjusted with sliders and then they are fixed in the position after adjusting them ...

when t changes from 0 to 1 ... B° moves on a circular curve with Center A ... It can move clockwise or anti-clockwise ... depending wheter B or A is "higher" ...

thanks for the help ...