Hi Patrick,
I think that your thread should be in "AutoCAD General Forum" because the question doesn't have to be a 3D related issue.
And try this.
It draws a tangent line from arc to arc.
Code:
(defun c:TANGENT_LINE (/ OSMODE_0 Pt01 Pt02 Entity1)
(setq OSMODE_0 (getvar "osmode"))
(setvar "osmode" 512)
(setq Pt01 (getpoint "Select 1st point on a circle: ")
Pt02 (getpoint "Select 2nd point on another circle: ")
); end of setq
(if (/= PEDITACCEPT 1)
(setvar "PEDITACCEPT" 1))
(command "._line" "_tan" Pt01 "_tan" Pt02 "")
(setq Entity1 (entlast))
(command "._pedit" Entity1 "e" "exit" "")
(setvar "osmode" OSMODE_0)
(princ)
); end of program