Keskikulma

Keskikulma is a Finnish term that translates to “central angle” in English. In geometry, it refers to the angle subtended by an arc of a circle at the circle’s center. The central angle is defined by two radii that connect the center to the endpoints of the arc.

If O is the center of a circle and A and B are points on the circle, the central angle is angle AOB. The measurement can be expressed in radians or degrees. The relationship between the central angle and the arc length s is s = rθ, where r is the circle’s radius and θ is the central angle in radians. Equivalently, in degrees, θ corresponds to a fraction of the full 360 degrees around the circle. The central angle is also linked to the inscribed angle subtending the same arc: the inscribed angle is half the measure of the central angle.

Key properties include that the central angle is determined solely by the arc it cuts out and is independent of the circle’s size. The radii forming the central angle define an isosceles triangle with the circle’s center at the apex, and the sum of central angles around a single point equals 360 degrees.

In practice, the term keskikulma appears mainly in mathematical contexts. It may also appear as a label or name in Finnish contexts, but it is primarily a geometric concept rather than a fixed geographic or administrative term. When encountered as a place name, verification from local sources is advised.