Circle: A circle is the locus of a point which moves in a plane in such a way that its distance from a given fixed point in the plane is always constant.Interior and Exterior of a circle: Let C(O, r) be a given circle. A point P is said to lie inside, outside or on the given circle according as OP < r, OP > r or OP = r respectively. All the points lying inside a circle are called its interior points and all those points which lie outside the circle are called its exterior points.
Circular region: The set of all points lying inside and on the circle C(O, r) is called a circular region .
Circumference of a circle: The perimeter of a circle is called its circumference.
Chord of a circle: A line segment joining two points on a circle is called the chord of the circle.
In the figure AS is the chord of a circle.
A chord passing through the centre of the circle is called a diameter of the circle.
Clearly, diameter = 2 ×radius.
![Circle and Types of Circle Assignment Help](https://www.expertsmind.com/../CMSImages/2450_circle2.jpg)
Congruence of circle: Two circles are said to be congruent if their radii are equal.
Arc of a circle: A continuous part of the circumference of a circle is called 'an arc of a circle.
![Circle and Types of Circle Assignment Help](https://www.expertsmind.com/../CMSImages/1195_circle3.jpg)
The arc PAO will be called a minor arc if l(PAO) < l(PBO) and will be called a major arc if l(PAO) > l(PBO).
Semi-circle: A diameter divides the circle into two equal arcs. Each of the two arcs is called a semi-circle.
Central angle: Let C(O, r) be any circle. Then any angle whose vertex is 0 is called a central angle.
Degree measure of an arc: The degree measure of an arc is the measure of the central angle containing the arc.
Congruent arcs: Two arcs of a circle (or of congruent circles) are congruent if the degree measure of the two arcs are the same.
Thus arc AB
arc CD if ÐAOB = ÐCOD and AOB = ÐCOD
Þ arc AB:; CD.
Segment of a circle: Let AB be a chord of the circle C (O, r). Then AB divides the circular disc into two parts. Each part is called a segment of the circle.
The segment containing the minor arc is called the minor segment and the segment containing the major arc is called the major segment of the circle.
![Circle and Types of Circle](https://www.expertsmind.com/../CMSImages/320_circle4.jpg)
The minor and major segments of a circle are called the alternate segments of each other.
Sector: A sector is that region of a circular disc C(O, r) which lies between an arc and the two radii joining the extremities of the arc and the centre .
![Circle Assignment Help](https://www.expertsmind.com/../CMSImages/871_circle5.jpg)
Secant of a circle: A line which intersects a circle in two distinct points is called a secant of the circle.
Tangent to a circle: A line is called a tangent line if it passes through two coincident points on the circle.
The point at which the tangent intersects the circle is called the point of contact.
![Circle and Types of Circle Assignment Help](https://www.expertsmind.com/../CMSImages/1424_circle6.jpg)
Concentric circle: Circles having the same centre and with varying radii are known as concentric circles.
![Math Help](https://www.expertsmind.com/../CMSImages/2174_circle7.jpg)
Cyclic quadrilateral: If all the four vertices of a quadrilateral, as in the figure below, lie on a circle, then such a quadrilateral is called a cyclic quadrilateral. If four points lie on a circle, then they are said to be concyclic.
![Mathematics](https://www.expertsmind.com/CMSImages/1016_circle8.jpg)
![Co-ordinate geometry](file:///C:/Users/print/AppData/Local/Temp/moz-screenshot.jpg)
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