Coefficients and equation of a line (perpendicular or parallel)
http://dmentrard.free.fr/GEOGEBRA/Maths/Export5/CoefdroitMD.html
http://dmentrard.free.fr/GEOGEBRA/Maths/Export5/CoefdroitMD.html
Information: Coefficients and equation of a line (perpendicular or parallel)