Declaration:  ExtendLine(p1x, p1y, p2x, p2y, Distance: Double; var p3x: Double; var p3y: Double; var p4x: Double; var p4y: Double);
Calculates the points to extend a line given by p1 and p2 a given Distance then returns the new points in variables p3 and p4.

Source Code:

var
  p3x, p3y, p4x, p4y: double;

begin
  ExtendLine(10, 10, 100, 100, 10, p3x, p3y, p4x, p4y); 
end;