Here is one way to draw it in AutoCAD.
I had initial difficulty in identifying angle alpha, because it was not labelled in the drawing. However I have plumped for the angle so marked in my picture.
I drew an arc alpha and trisected it by using Divide. I drew a line to the third point, and mirrored it about a vertical line through B. This line I extended to C. Then I drew a line from A through C and extended it to D.
Check measurement reveals that C-D equals A-B equals r.