Circles: Radius, Diameter & Circumference
What Is a Circle?
A circle is a perfectly round shape, like a pizza, a coin, or a hula hoop. Every point on the edge of the circle is the same distance from the centre.
Important Circle Parts:
1. Centre
The middle point of the circle.
2. Diameter
A line that goes across the circle, passing through the centre.
It's twice as long as the radius.
👉 It’s the longest straight line you can draw inside a circle.
3. Radius
A line from the centre to the edge of the circle.
It's half the length of the diameter.
What is Circumference?
The circumference is the distance around the edge of the circle. It's like the circle’s version of a perimeter.
Formula for Circumference
There are two ways to find the circumference:
1) If you know the diameter (d):
Circumference = π × diameterorC = π × d
2) If you know the radius (r):
Circumference = 2 × π × radiusorC = 2πr
Unit of Circumference can be cm,meter, km, mm, etc.
🌟 What is π (pi)?
Pi (Ï€) is a special number in maths.
It’s about 3.14, but it goes on forever!
You can use 3.14Â in most questions unless told otherwise.
🎯 Top Tips:
🌟 Diameter is twice the radius. So if you know one, you can find the other!
🌟 Always check if the question gives you the radius or the diameter.
🌟 Use 3.14 for π unless your calculator has a π button.
🌟 The circumference is like the fence around a circular garden—it tells you how far it is around.
