Subtend

To subtend means to extend under, or to form the base of an angle, shape, or arc. This concept is often encountered in geometry and optics, describing the line segment joining two points on a curve or the angle formed at a specific point by two other points. It is a technical term illustrating the geometric relationship of lines, angles and curves. The angle a line subtends increases with the length of that line as you move from one point to the other. It’s a key principle in understanding perspective and the visual size of objects.

Subtend meaning with examples

• The arch of the bridge subtends a large angle at the viewer's position. The greater the distance between the arch's endpoints, the larger the angle. The architectural design cleverly uses subtended angles to create an illusion of grandeur. The perceived size depends on the subtended angle, thus creating different viewpoints for its use in design.
• In a visual display, the pixel subtends a small angle relative to the viewer's eye. The closer the viewer is to the screen, the larger the subtended angle. This is fundamental to understanding screen resolution and image clarity. A larger angle is required to achieve a desired image quality, with higher resolution ensuring clearer images.
• From the observer's location, the diameter of the full moon subtends a very small angle. The apparent size is determined by this angle of sight, as the moon covers a small portion of the viewer's field of vision. This explains why the moon and sun appear similar in size. The subtended angle is the key visual measurement here.
• A chord of a circle subtends a specific angle at the circle's center. The length of the chord influences this angle. This concept is critical in understanding circle properties in geometry. The relationship shows how various points on a circle relate in terms of shape and size.