01 Key Concepts
Radius
The distance from the center of a circle to any point on the circle.
Diameter
The distance across the circle through its center; the diameter is always twice the radius.
Circumference
The distance around the outside of a circle, calculated as 2*pi*r or pi*d.
Area of a Circle
The space enclosed by a circle, calculated as pi*r^2.
Chord, Arc, and Sector
A chord connects any two points on the circle. An arc is a portion of the circle's edge. A sector is a 'pie slice' region bounded by two radii and an arc.
02 Key Formulas
- Circumference = 2*pi*r = pi*d
- Area = pi*r^2
03 Solved Examples
Example 1 Find the circumference of a circle with radius 7 (use pi ~ 3.14).
- Circumference = 2*pi*r = 2*3.14*7.
- = 6.28*7.
Answer: Approximately 43.96 units
Example 2 Find the area of a circle with radius 5 (use pi ~ 3.14).
- Area = pi*r^2 = 3.14*5^2 = 3.14*25.
Answer: 78.5 square units
Example 3 A circle has diameter 20. Find its radius and circumference (use pi ~ 3.14).
- Radius = diameter/2 = 20/2 = 10.
- Circumference = pi*d = 3.14*20.
Answer: Radius = 10, Circumference = 62.8 units
04 Practice Questions
1Find the circumference of a circle with radius 10 (pi~3.14).
62.8
2Find the area of a circle with radius 4 (pi~3.14).
50.24
3A circle has diameter 14. Find its radius.
7
4Find the area of a circle with radius 3 (pi~3.14).
28.26
5What is a 'chord' of a circle?
A segment connecting any two points on the circle
📄 Circles — Downloadable Worksheet
10 questions with a full answer key. Grab the PDF to print, or try the interactive version in your browser.