Useful Definitions
arc: a curved line that is part of the circumference of a circle chord: a line segment within a circle that touches 2 points on the circle. circumference: the distance around the circle. diameter: the longest distance from one end of a circle to the other. origin: the center of the circle pi (): A number, 3.141592…, equal to (the circumference) / (the diameter) of any circle. radius: distance from center of circle to any point on it. sector: is like a slice of pie (a circle wedge). tangent of circle: a line perpendicular to the radius that touches ONLY one point on the...
Learn MoreIntroduction to circles
Definition: A circle is the locus of all points equidistant from a central point. A circle is a type of line. Imagine a straight line segment that is bent around until its ends join. Then arrange that loop until it is exactly circular – that is, all points along that line are the same distance from a center point. There is a difference between a circle and a disk. A circle is a line, and so, for example, has no area – just as a line has no area. A disk however is a round portion of a plane which has a circular outline. If you draw a circle on paper and cut it out, the round piece...
Learn MoreChords & Radii
All the “parts” of a circle, such as the radius, the diameter, etc., have a relationship with the circle or another “part” that can always be expressed as a theorem. The two theorems that deal with chords and radii (plural of radius) are outlined below. 1. If a radius of a circle is perpendicular to a chord, then the radius bisects the chord. Here’s a graphical representation of this theorem: 2. In a circle or in congruent circles, if two chords are the same distance from the center, then they are...
Learn MoreCircumference
One last thing that has to be discussed when dealing with circles is circumference, or the distance around a circle. The circumference of a circle equals 2 times PI times the measure of the radius. That postulate is usually represented by the following equation (where C represents circumference and r stands for radius): C = 2(PI)r. For example, if a circle has a radius of 3, the circumference of the circle is 6(PI). Also, you can find the length of any arc when you know its degree measure and the measure of a radius with the following formula (L = length, n = degree measure of arc, r =...
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