It's best shown by an image:
(image)
where the angle $A$, $B$, and $C$ can be any known angle and the lengths of the line segments that make up the triangle can be any known length and line $x$ would be the only unknown. Line $x$ would also be exactly twice the length from where angle $B$ would intersect line segment $AC$.
I know there is a formula for when it is a right triangle, but I'm wondering if there is one for a non-right triangle, or if there needs to be extra information.
