**Definition of Circle:** The set of all points in one plane that in a fixed distance from a center.

**Definition of Center:** Center of a Circle is a point inside the circle and is at an equal distance from all of the points on its circumference.

Example of centre:

O is a centre of above circle.

## Radius, Diameter, Circumference:

**Radius:** The radius is the distance from the center to the edge.

**Diameter:** The diameter starts at one side of the circle, passes through the center ends on other side.

or, if that line passes through the center it is called a Diameter.

**Circumference:** The circumference is the distance around the edge of the circle.

Here ABC is the circumference of the circle.

**Chord:** A line that goes from one point to another on the circle’s circumference is called a Chord.

Here AC is chord of that circle.

**Arc:** An a part of the circumference is called an Arc.

*****Some important information*****

***** A straight line cannot intersect a circle in more than two points.**

***** Chords equidistant from the centre of a circle are equal.**

***** The diameter is the greatest chord of a circle.**

***** Equal chords of a circle are equidistant from the centre.**

***** The angle subtended by the same arc at the centre is double of the angle subtended by it at any point on the remaining part of the circle.**

***** Angles in a circle standing on the same arc are equal.**

***** The angle in the semi- circle is a right angle.**

***** The sum of the two opposite angles of a quadrilateral inscribed in a circle is two right angles.**

***** A parallelogram inscribed in a circle is a rectangle.**

***** If two opposite angles of a quadrilateral are supplementary, the four vertices of the quadrilateral are con-cyclic.**

***** In same circle radius are equal.**

*****Add between centre and arc is called radius.**

## ***Some M.C.Q question***

1.Look at the circle below. The line segment appears to be

a.an arc b. a perimeter c. a radius d. a diameter

2. Line segment AB is what part of this circle?

a.circumference b. radius c. diameter

3. Is the shape flat or solid?

a.flat b. solid

4. Write the name of the following using the circle below:

Name of the circle : —————

Diameter :———————-

Radius;————————-

Chord:————————-

5. What is this measurement called?

a. Area b. Circumference c. Diameter d. Radius

6. (a) What type of angle is CAB?

a. Acute b. obtuse c. right d. straight

(b) What type of angle AOB?

7. In circle O, which is the chord?

a. AB b. OD c. AC d.AO