A circle is a simple 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 center; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant.

1. Basic Concepts of
Prepared By
Ronnith Nandy

2. Circle is a simple shape of Euclidean geometry that is
the set of points in the plane that are equidistant from
a given point, the centre.
A circle is a simple closed curve which divides the
plane into 3 regions: Interior, Exterior and On
In everyday use, the term
"circle" may be used
interchangeably to refer to
either the boundary of the
figure, or to the whole figure
including its interior; in strict
technical usage, the circle is
the former and the latter is
called a disk.

3. The word "circle" derives from the Greek, kirkos "a
circle," from the base Ker- which means to turn or
bend.
Circle was created long before recorded history. It is
quite likely that it was drawn by a stick in the sand.
With the sun being a constant in early man’s
existence and the source of all life, it is quite likely
that the first circle represented the sun.
Circle has evolved substantially
with Euclidean geometry being
its crowning point of
technological understanding,
Without circles, there would be
no wheel, which is man’s
crowning achievement dating
back to the Neolithic Age (circa
9500 BC).

4. Parts of a Circle

5. CIRCLE TERMINOLOGY
CIRCUMFERENCE
The Circumference of a circle (from "circa",
the Latin word for "around") is the distance around
the edge of the circle.

6. CIRCLE TERMINOLOGY
RADIUS
In classical geometry, the radius of a circle or sphere
is the length of a line segment from its center to its
perimeter. The name comes from Latin radius,
meaning "ray" but also the spoke of a chariot wheel.

7. CIRCLE TERMINOLOGY
CHORD
A chord of a circle is a straight line segment whose
endpoints both lie on the circle. A secant line, or
just secant, is the infinite line extension of a chord.
More generally, a chord is a line segment joining two
points on any curve, for instance an ellipse.

8. CIRCLE TERMINOLOGY
DIAMETER
The diameter of a circle is any straight line segment
that passes through the center of the circle and
whose endpoints lie on the circle. It can also
be defined as the longest chord of the circle.

9. CIRCLE TERMINOLOGY
ARC
The arc of a circle is a portion of the circumference
of a circle. Measure an arc by two methods: 1) the
measure of the central angle or 2) the length of
the arc itself.

10. CIRCLE TERMINOLOGY
SEGMENT
The segment of a circle is the region bounded by a
chord and the arc subtended by the chord.

11. CIRCLE TERMINOLOGY
SECTOR
A circular sector or circle sector (symbol: ⌔), is the
portion of a disk enclosed by two radii and an arc,
where the smaller area is known as the
minor sector and the larger being the major sector.

12. PROPERTIES OF CIRCLE
In geometry, a large number of facts about circles and
their relations to straight lines, angles
and polygons can be proved. These facts are called
the properties of the circle.
Circles having equal radii are congruent.
Circles having different radii are similar.
The central angle which intercept an arc double of
any inscribed angle that intercepts the same arc.
The radius perpendicular to a chord bisects the
chord.
The chords equidistant from the center are equal in
length.
A tangent to a circle is at right angles to
the radius at the point of contact.
Two tangents drawn to a circle from a point out side
are equal in length.
The angle subtended at the center of a circle by its
circumference is equal to four right angles.

13. PROPERTIES OF CIRCLE
In geometry, a large number of facts about circles and
their relations to straight lines, angles
and polygons can be proved. These facts are called
the properties of the circle.
Circumference of two different circles is
proportional to their corresponding radii.
Arcs of the same circle are proportional to their
corresponding angles.
Radii of the same circle or the equal circles are
equal.
Equal chords have equal circumferences.
The diameter of a circle is the longest chord.
Circle which have equal radii are equal.
Equal circles have equal circumference.