ok, I'll take the easy route.
Draw a line X any length from A to B
Draw a circle at A of diameter 0.5*X
Draw a circle at B of diameter 0.5*X
Draw a circle using TAN, TAN, RADIUS from Circle 1 to Circle 2 and enter same radius as previous
Now draw line from A to first & second circles intersection, the to second & third circles intersection, then to point B
if I had time I would code it but ...