Perpendicular lines

Perpendicular lines intersect to form four right angles. In Euclidean geometry, their slopes are negative reciprocals when both slopes are defined.

Angle: A geometric figure formed by two rays or lines sharing an endpoint or intersection. Perpendicularity is defined by the measure of the angles formed at the intersection.
Negative reciprocal: For a nonzero number, its negative reciprocal is the negative of its multiplicative inverse. The slopes of two nonvertical perpendicular lines are negative reciprocals.
Cartesian coordinate system: A system that locates points using signed distances from mutually perpendicular coordinate axes. Its perpendicular axes let coordinates represent horizontal and vertical directions separately.
Parallel lines: Coplanar lines that never intersect and remain the same distance apart. Parallel lines do not meet, while perpendicular lines intersect at right angles.
Right angle: An angle measuring exactly 90 degrees, or π/2 radians. Each of the four angles formed by perpendicular lines is a right angle.
Dot product: An operation on vectors that returns a scalar equal to the product of their magnitudes and the cosine of their angle. Direction vectors are perpendicular exactly when their dot product is zero.
Orthographic projection: A method of representing three-dimensional objects by projecting them onto planes along perpendicular directions. Perpendicular projection preserves true dimensions in technical drawings.
Oblique lines: Lines that intersect at an angle other than 90 degrees. Oblique intersections distinguish perpendicularity from intersection in general.
Intersection: A point or set of points shared by two or more geometric objects. Two perpendicular lines meet at their shared intersection point.
Perpendicular bisector: A line that passes through a segment's midpoint at a right angle to the segment. It combines perpendicularity with the midpoint condition to locate equidistant points.

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