en.wikipedia.org/wiki/Orthogonality

The line segments AB and CD are orthogonal to each other. In mathematics,
orthogonality is the relation of two lines at right angles to one another ...

www.artyfactory.com/perspective_drawing/perspective_3.html

There are two types of construction lines used in this perspective drawing: 1)
ORTHOGONAL LINES which we have drawn in RED. 2) TRANSVERSAL LINES
...

mathworld.wolfram.com/OrthogonalLines.html

Orthogonal Lines. Two or more lines or line segments which are perpendicular
are said to be orthogonal. ... CITE THIS AS: Weisstein, Eric W. "Orthogonal Lines.

drawsketch.about.com/od/drawingglossary/g/orthogonal.htm

Jan 11, 2017 ... Artists talk about 'orthogonal lines' as these are key to drawing with correct
perspective. Explore orthogonal and transversal lines with an easy ...

www.creativeglossary.com/art-perspective/orthogonal-lines.html

Definition of orthogonal lines at CreativeGlossary.com.

www.olejarz.com/arted/perspective/yorth.html

Drawing in One-Point Perspective is a step-by-step guide to one-point perspectie
drawing. Created by Harold Olejarz, the site demonstrates how to draw a ...

www.coolmath.com/algebra/08-lines/14-perpendicular-lines-01

Let's graph these lines: * I'm using y = mx + b stuff to graph them!

math.tutorvista.com/geometry/orthogonal-lines.html

When two lines intersect at right angles to each other, they are said to be
orthogonal. If the slope of the first line is m1 and the slope of the second line is m
2, then ...

www.purplemath.com/modules/slope2.htm

Parallel lines and their slopes are easy. Since slope is a measure of the angle of
a line from the horizontal, and since parallel lines must have the same angle, ...

www.mathopenref.com/coordperpendicular.html

When two lines are perpendicular to each other (at right angles or 90°), their
slopes have a particular relationship to each other. If the slope of one line is m
then ...