condition of orthogonality

Let two straight lines of the $xy$-plane have the slopes $m_{1}$ and $m_{2}$.  The lines are at right angles to each other iff $m_{1}$ and $m_{2}$ are the opposite inverses of each other, i.e. iff (http://planetmath.org/Biconditional)

 $m_{1}m_{2}=-1.$

Example.  The lines  $y=(1+\sqrt{2})x$  and  $y=(1-\sqrt{2})x$  are at right angles to each other.

 Title condition of orthogonality Canonical name ConditionOfOrthogonality Date of creation 2013-03-22 14:48:05 Last modified on 2013-03-22 14:48:05 Owner pahio (2872) Last modified by pahio (2872) Numerical id 14 Author pahio (2872) Entry type Result Classification msc 15A57 Classification msc 51F20 Synonym condition of perpendicularity Related topic OrthogonalCurves Related topic InverseNumber Related topic OppositeNumber Related topic NormalLine Related topic AngleBetweenTwoLines Related topic PerpendicularityInEuclideanPlane Related topic Evolute2 Related topic ExampleOfFindingCatacaustic Defines opposite inverse