Perpendicular Lines - Geometry Made Easy - Definition of perpendicular
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Perpendicular Lines

Perpendicular lines
Perpendicular lines

Two lines are perpendicular if they cross at right angles. You can test this by extending the lines until they cross (if they do not cross then they are parallel). Where the two lines cross, draw a right triangle, and then see whether the triangle conforms to the Pythagorean Theorem - if so, then your lines are crossing at a right angle, and they are perpendicular.

If Line A and Line B are both perpendicular to Line C, then Line A and Line B have to be parallel to each other.

All right triangles are made from two perpendicular line segments. The corners of rectangles (and squares) are also made of perpendicular line segments.

Perpendicular planes
Perpendicular planes

Two planes can also intersect at right angles, and then they are perpendicular planes. The sides of a cube are perpendicular planes.

Parallel lines
More about Lines
More about Geometry

Bibliography and further reading about geometry:

More about Geometry
More Easy Math
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Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

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