when I creat a 3 point curve on another body, using its points , when I want to redimension the Radius, the curve displaces, but in the tutorial https://youtu.be/20hLhQHKESU?t=2m28s
it does not happen , how ?
Hello. You will notice in the tutorial that the start and finish points of the arc are colored black. This means that they are fixed or they have relations that prevent them from moving, The simplest way is to position the arc and then make the 2 points fixed.
The points in the tutorial are creating relations automatically. Make sure your bottom point has a midpoint relation with the bottom edge and the top point is coincident with the leftmost point across from the origin. If you are not creating the relations automatically they will move when you change the radius. You can turn automatic relations on/off in Tools>Sketch Settings> Automatic Relations.