Triangle bisection on non-right angle triangle with known angle and two sides I'm creating 3D road intersections and to create the corner points I detect when the edge vectors of the road intersect. It's extremely accurate.
However, I would like to pre-calculate the corner positions instead. The interior angles of the intersection are all known and are never 90 degrees.
I've boiled it down to this 2D problem where side a and b are always known and the angle specified is random but always known. A and B will always equal each other. Everything else is unknown:

How do I get the length of line D (bisect)?

If the triangle is isosceles, then the intersection of the lines D and the line C forms a right angle and so
$$ D = B \cos\left(\dfrac{\theta}{2}\right) $$ 
