how do we define circles?

How Do We Define Circles?

Circle

A circle is the set of all points in a plane at given distance froma given point.

http://www.math.com/school/subject3/lessons/S3U1L6GL.html

-Given distance is the radius

- point is called the center

Chord

A line segment that connects two points on a circle 

http://en.wikibooks.org/wiki/Geometry/Chapter_7

Diameter

A line segment through the center with endpoints on the circle

http://openhighschoolcourses.org/mod/book/view.php?id=258&chapterid=500

Tangent

A line that touches a circle in exactly one point.

http://www.icoachmath.com/math_dictionary/Common_External_Tangent.html

-Congruent circles have the same radius

-Concentric circles have the same center

Semicircle

half a circle= 180 degrees

Minor Arch- less than 180 degrees

Major Arch- more than 180 degrees