Table of Contents

Last modified on August 6th, 2021

A closed, round geometric figure in which the set of all the points in the plane is equidistant from a given point called ‘center’.

**1) Radius** – The
line that joins the center of the circle to the
outer boundary. It is usually represented by ‘** r**’ or ‘

**2) Diameter – **The line segment whose endpoints lie on the
circle and that passes through the center. Its length is twice the length of a
radius. It is represented by as -‘** d**’ or ‘

So, *r* = *d*/2 or *R* = *D*/2

**3) Chord – **The line segment whose endpoints lie on the circle,
thus dividing a circle into two regions. The diameter is the longest chord of a
circle.

**4) Secant – **An extended chord that cuts the circle at two distinct points.

**5) Arc – **The connected section of the circumference of a
circle.

**6) Tangent – **A line that touches the circumference of a circle at a
point.

**7) Sector – **A region bounded by two radii of equal length with a
common center.

**8) Segment** –
The segment of a circle is the region bounded by a
chord and the arc subtended by the chord.

Also known as the perimeter, it is the total distance covered around the circle. The formula is given below:

**Circumference ( C) = 2πr**, here

**Problem:** Finding the circumference of a circle when only the **DIAMETER** is known

**The diameter of a circle is 6 centimeters. Find the circumference**

Solution:

As we know,** C = 2πr**, here

Hence, C = 2 x 3.14 × 3

= 18.84 cm

**Problem:** Finding the circumference of a circle when only the **RADIUS** is known

**The radius of a circle is 4 inches. Find the circumference**

Solution:

As we know,** C = 2πr** , here

= 2 × 3.14 × 4

= 25.12 inches

It is the total space enclosed inside the boundary of the circle. It is also known as the ‘surface area of the circle’. The formula is given below:

**Area ( A) = πr^{2}**, here

**Problem:** Finding the area of a circle when only the **RADIUS** is known

**Find the area of a circle with a radius of 9 cm**

Solution:

As we know,** A = πr^{2}**, here

= 3.14 × 9 × 9

= 254.34 cm

**Problem:** Finding the area of a circle when only the **DIAMETER** is known

**Find the area of a circle with a diameter of 10 cm**

Solution:

As we know,** A = πr^{2}** and

= 3.14 × 5 × 5

= 78.5 cm

**More Resources**- Area of a Circle
- Circumference of a Circle
- Equation of a Circle
- Diameter of a Circle
- Radius of a Circle
- Concentric Circles
- Semi circle
- Chord of a Circle
- Tangent of a Circle
- Arc of a Circle
- Secant of a Circle
- Sector of a Circle
- Center of a Circle
- Segment of a Circle
- Inscribed and Circumscribed Circles
- Quadrant of a Circle
- Congruent Circles
- Unit Circle
- Parametric Equation of Circle

Last modified on August 6th, 2021