I recently offered to help a colleague with some 3d maths saying that if the sketch entities turned black then a solution could be found for the limited available information. So I sketched up his problem and the sketch solved.

He then asked if I could tell him how the calculations were done.

I can't but I hope someone can.

I can supply details of the problem if anyone wants.

Thanks in anticipation.

Please post it here.

The answer is probably the fact that SolidWorks is a virtual reality medium. If I draw a line 20" long in a sketch, that would be similar to having a rod cut to length at 20". Now, if I weld that rod to others, also predefined in length, at predefined angles and attach them to the ground (read the origin) I will get a rigid, immovable part.

So there is no calculation involved, you just mirror what you would do in real life.