en.wikipedia.org/wiki/Circle

A circle is a simple closed shape in Euclidean geometry. It is the set of all points
in a plane that are at a given distance from a given point, the centre; equivalently
...

www.khanacademy.org/math/geometry-home/cc-geometry-circles

Explore, prove, and apply important properties of circles that have to do with
things like arc length, radians, inscribed angles, and tangents.

www.regentsprep.org/regents/math/geometry/gp15/circleangles.htm

Circles - angles formed by radii, chords, tangents, secants. ... Tangents, Secants
Topic Index | Geometry Index | Regents Exam Prep Center ... An inscribed angle
is an angle with its vertex "on" the circle, formed by two intersecting chords.

www.mathplanet.com/education/geometry/circles/basic-information-about-circles

A circle is all points in the same plane that lie at an equal distance from a center
point. The circle is only composed of the points on the border. You could think of
...

mathbitsnotebook.com/Geometry/Circles/CRAngles.html

MathBitsNotebook Geometry CCSS Lessons and Practice is a free site for ... In a
circle, or congruent circles, congruent central angles have congruent arcs.

amsi.org.au/teacher_modules/Circle_Geometry.html

The theorems of circle geometry are not intuitively obvious to the student, in fact
most people are quite surprised by the results when they first see them.

www.mathsisfun.com/geometry/circle-theorems.html

Some interesting things about angles and circles. ... Inscribed Angle: an angle
made from points sitting on the circle's circumference. A and C ... Geometry Index.

www.math.com/tables/geometry/circles.htm

Circles. (Math | Geometry | Circles) ... arc: a curved line that is part of the
circumference of a circle ... Circumference of Circle = PI x diameter = 2 PI x radius

www.ixl.com/math/geometry/area-and-circumference-of-circles

Fun math practice! Improve your skills with free problems in 'Area and
circumference of circles' and thousands of other practice lessons.

illuminations.nctm.org/Lesson.aspx?id=2160

Using a MIRA<sup>TM</sup> geometry tool, students determine the relationships ... Finding
the circumference or area of a circle depends on the diameter of the circle.