kohtisuoraa

Kohtisuoraa is a term used in geometry to describe a relation in which two objects meet at a right angle of 90 degrees. It can refer to perpendicular lines, or to a line that is perpendicular to a plane. In Finnish, kohtisuora translates to perpendicular, and the noun form refers to the lines or lines and planes that satisfy this condition.

In the plane, two lines are perpendicular if they intersect and form four right angles. If the lines have slopes m1 and m2 and neither line is vertical, they are perpendicular when m1 times m2 equals -1. If one line is vertical, the perpendicular line is horizontal, and vice versa. A common vector approach is that two direction vectors are perpendicular when their dot product is zero.

In three-dimensional space, two lines are perpendicular only if they intersect and their direction vectors are perpendicular (their dot product is zero). If the lines do not intersect (they are skew), they are not considered perpendicular in the standard sense. A line and a plane are perpendicular when the line intersects the plane and is perpendicular to every line in the plane that passes through the intersection point; equivalently, the line is parallel to the plane’s normal vector.

Applications of kohtisuoraa include solving right-angle problems, constructing perpendiculars in coordinate geometry, and describing orientations in engineering and graphics. The concept also underpins the definition of perpendicular distance, projections, and many geometric theorems involving right angles. The term is common in Finnish geometry texts and is used similarly across European mathematical traditions.