Note that a diameter is a chord (the longest possible chord of a circle!). Interested in learning more? Why not take an online Geometry course?Īny line segment connecting two points on the circle is called a chord. The arc A in the diagram below is shown as a bold line, and the sector S is shown as a shaded area.
The sector is the area enclosed by the arc and the radii. The arc is the portion of the circle opposite to (or subtended by) the angle α and between the endpoints of the radii. The line segment that connects them passes through the center and is called the diameter of the circle.Īny two radii in the circle (which form an angle α), such as those shown below, form an arc and a sector. Given any point P 1 on the circle, the most distant point P 2 that is also on the circle is on the exact opposite side, and these points are the length of two radii apart. We can also identify other parts of a circle. We can also define angles with either positive or negative numbers, depending on the direction of measurement from a particular radius-a positive angle is traditionally measured in the counterclockwise direction, and a negative angle is traditionally measured in the clockwise direction, as shown below. Using our measurement of degrees, this angle α can (unambiguously) be any value between 0° and 360°. The circle itself does not show any angles or sides that we can use to determine how many degrees are in the figure (as we did with polygons), but we can see that any two radii do form an angle α, as shown below.
Each of the line segments drawn from C to the circle is called a radius (in other words, no one segment is defined as the radius, since all such segments are equal in length). Note that regardless of which point on the circle is chosen, it is always a distance r from the center point, C. A circle with a radius r and center point C is shown below. The distance from the center of the points that lie on the circle is called the radius (plural radii) of the circle. Thus, we can define a circle (without a definite location) by specifying the distance from the center alternatively, we can define a circle (with a definite location) by specifying the distance from and the location of the center. O Calculate the area and circumference of a circle or portion thereofĪ circle is simply a figure defined by all the points that are equidistant from a given center point.
#Circle geometry how to#
O Know how to fundamentally define a circle
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