Properties of Circles - Grade 6

Unit Circle

A circle at the origin (0, 0) and has a radius of one centered on the coordinate plane system

Tangent Line

A line in the plane of a circle that intersects the circle in exactly one point.

chord

A line segment with both endpoints on the circle. Always shorter than the diameter.

secant

A line that intersects a circle at exactly two points.

sector

A part of a circle enclosed by tow radii and an arch connecting them

arc length

A portion of the circumference of a circle named and measured by its endpoints

radius

A straight line from the center to the edge of a circle or sphere. The radius is half the diameter.

diameter

A straight line passing from side to side through the center of a circle or sphere. The diameter is twice the radius.

central angle

An angle formed by two radii of a circle and whose vertex is the center of the circle.

inscribed angle

An angle whose vertex is on a circle and whose sides contain chords of the circle.

reflex angle

Between 180 and 360 degrees.

Tangent Circles

Circles (also known as kissing circles) are circles in a common plane that intersect in a single point.

semi circle

Half of a circle.

circle

Is the set of points which are all the same distance (its radius) from the center.

center

Mid-point of a circle.

pi (π)

The Greek letter used to represent the ratio of the circumference to the diameter of a circle.

36

The central angle measure is _______ degrees when the sector of a circle makes up 10% of the circle. (10% of 360 degrees)

108

The central angle measure is _______ degrees when the sector of a circle makes up 30% of the circle. (30% of 360 degrees)

252

The central angle measure is _______ degrees when the sector of a circle makes up 70% of the circle. (70% of 360 degrees)

vertex

The common endpoint of an angle.

circumference

The distance around a circle. C = πd

360

The number of degrees in a circle

90

The the central angle measure is _______ degrees when the sector of a circle makes up 25% of the circle? (25% of 360 degrees)

180

What is the central angle measure is _______ degrees when the sector of a circle makes up 50% of the circle. (50% of 360 degrees) in this circle it would be section "A".