Thanks, I see how it works now (and why I got circles ) , much easier to join the two points directly by applying a tangent. However I just tested and find that the end result will be the same as I could confirm that the coincident constraint is automatically deleted when the tangent is applied. In the following screen capture I had just applied coincidence constraints between the lines and the arc and then selected the line an arc ready do apply tangent. The next screenshot shows how the coincidence constraint is automatically deleted and reported in a message box. Again it is more complicated than needed and your advice is well taken, but it should not cause any ill effects. And if one initially draws a line and an arc so that they coincides (thus a coincident constraint is automatically created), it is good to know that it is removed once the tangent is applied):chrisb wrote: ↑Sat Jul 07, 2018 3:15 pmThat's exactly how it happens. From a geometric point of view it is no problem to have both, because the coincident point lies on both connected lines and lies thus on a tangent of both. However internally there can rise problems because the points are represented with finite precision.When doing the edits sometimes line endpoints get disconnected from each other and it is necessary to connect again by applying a coincident constraint (perhaps that is where you point out that tangency can be applied directly?).
That's why you should select the endpoints when applying tangency in these cases.