Kulmaepäsuorat

Kulmaepäsuorat is a term used in Finnish geometry to refer to angles that are not right angles. The word is formed from kulma (angle) and epäsuora (not straight/oblique). In standard school geometry, angles are commonly categorized as terävä (acute, less than 90 degrees), oikea (right, 90 degrees) and tylppä (obtuse, greater than 90 and less than 180 degrees). Kulmaepäsuorat is a broader label that covers both acute and obtuse angles, i.e., all angles with measures between 0 and 180 degrees that are not 90 degrees. Angles of 0 degrees or 180 degrees are degenerate and typically not counted as ordinary angles.

When two lines intersect, they form a pair of equal vertical angles; the term kulmaepäsuorat would apply to any of the non-right interior angles formed by the intersection, depending on which measure is taken.

Context and usage: The term is not as standard as terävä and tylppä in Finnish educational materials; some authors prefer to use the precise categories terävä and tylppä and reserve kulmaepäsuorat for when a non-specific reference to non-right angles is intended.

See also: right angle (oikea kulma), acute angle (terävä kulma), obtuse angle (tylppä kulma), straight angle (suora kulma).