if you extend the three sides of the triangle such that the triangle sides
are now line segments of these lines, then, there are 3 circles that touch one side of the triangle tangentially
and touch the extended lines tangentially.
If you bisect the appropriate external angle you will have a line whose points are
the same perpendicular distance from the extended line and a side of the triangle.
Do the same for the other relevant extended line and you will find the centre of the circle with centre D (of which there are 3).
That can get you started geometrically.