Desargues Configuration

Drag the blue colored point.
If two triangles are so situated that line joining the pair of corresponding vertices are concurrent then the points of intersection of pair of corresponding sides are collinear and conversely. This theorem can be stated as “if two triangles are central couple then they are axial couple and conversely”. The Desargues theorem can also be stated as “if two triangles are perspective from a point then they are perspective from a line and conversely”.