My question is how to draw a line from a tangent point over a
> circle or arc, to another point? How can i resolve it?
should be simple : in a sketch, draw the arc, draw the point, draw the line then add the constraints. Or did I misunderstood you ?
The second question is, if i sketch a text and extrude it
> suddenly the regeneration or reconstuction of the design goes
> very slowly
texts generates hundreds, or even thousands of faces... "suppress" the extrusion feature until you really need it.