Maxwell's theorem in plane geometry states that, given a triangle 
, a point 
, and a triangle 
whose sides 
, 
, and 
are respectively parallel
to 
,
, and 
, the lines through 
, 
, and 
respectively parallel to 
, 
, and 
are concurrent.
The theorem is a formulation using parallel lines of the reciprocal property of orthologic triangles: if the lines from the vertices of one triangle perpendicular to the opposite sides of another are concurrent, then the three lines in the reverse direction that are perpendicular to the sides of the first triangle are also concurrent.
