Perpendicular

Two lines, vectors, planes, etc., are said to be perpendicular if they meet at a right angle. In , two vectors and are perpendicular if their dot product

(1)

In , a line with slope is perpendicular to a line with slope . Perpendicular objects are sometimes said to be "orthogonal."

In the above figure, the line segment is perpendicular to the line segment . This relationship is commonly denoted with a small square at the vertex where perpendicular objects meet, as shown above, and is denoted .

Two trilinear lines

			(2)
			(3)

are perpendicular if

(4)

(Kimberling 1998, p. 29).