Posted by dellus on Dec 14, 2018; 12:48am
URL: https://forum.librecad.org/polyline-creation-tp5716736p5716741.html

I thought your figure was something like a half-moon, crescent!
Anyway, if you zoom in and in very close at the junction points of the arcs you will see that they don't meet, by about 0.001 or 0.0001 units if you measure it. You said you have calculated the points, this might be the source of the inaccuracy, as the output of circle or ellipse calculation is being rounded. So avoid to use calculated values or positions, instead try to solve everything geometrically with CAD.
You can't always fix such discrepancies with "Trim", because not all arcs do meet somewhere when lengthening them.
Maybe you have to reconstruct your shape considering all this, if I am on the right trace.