Hi folks.
If you specify 2 sides for the arc, you will indeed get an angle.
This can be used as a trick to get a real fast 90° angle if you use the "Half circle" inference. Then, each side of the angle is at 45° from the axis of the angle. This is a qucik way of drawing roofs with a 45° slope. Add a base line to the arc to get a triangle and push it with the "Push/Pull" Tool. However, the apex will be smoothed and thus, will require unsmoothing.
Just ideas.