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Two lines, vectors, planes, etc., are said to be perpendicular if they meet at a Right Angle. In $\Bbb{R}^n$, two Vectors ${\bf A}$ and ${\bf B}$ are Perpendicular if their Dot Product

{\bf A}\cdot {\bf B}=0.

In $\Bbb{R}^2$, a Line with Slope $m_2 = -1/m_1$ is Perpendicular to a Line with Slope $m_1$. Perpendicular objects are sometimes said to be ``orthogonal.''

In the above figure, the Line Segment $AB$ is perpendicular to the Line Segment $CD$. This relationship is commonly denoted with a small Square at the vertex where perpendicular objects meet, as shown above, and is denoted $AB\perp CD$.

See also Orthogonal Vectors, Parallel, Perpendicular Bisector, Perpendicular Foot, Right Angle

© 1996-9 Eric W. Weisstein