This is a description of a procedure done in a CAD program.  
I have yet to check the maths behind the construction as there seems to be some issues of precision.

Around the origin O, inscribe 4 concentric circles of radius 1,2,3 and 4
Draw a radial line within the innermost circle to a point A on the circumference.
Perpendicular to it draw a radius to the outer circle (r=4).
At the midpoint of that radius (intersection with the second inner circle - "+" symbol) inscribe a circle of radius = 2.
This circle intersects the third circle in two places. Let B be the intersection further from A.
Join A and B.  Using B as the centre and radius AB construct a circle.  This circle intersects the outer circle in two places . Let C be the intersection closer to A.  Create the line AC and BC.
The angle bisectors of the triangle intersect  at D on the the circumference of the circle of radius =2.
OA=1, OB = 3, OC= 4 and OD = 2.

D is slightly to the right of the "+" symbol.  You have to imagine the circles, too hard to draw!

                                      O ___ A
                                       |
                                       |
                                       +  D
                              B       |
                                       |            C
                                       |

Posted by brianjn on 2012-03-25 00:26:14