What do these things have in common?
They're all circles.
A circle is a closed shape made of a perfectly curved line.
A circle has a point inside it, called the center.
The distance from the center of a circle to any point on the edge is called the radius.
All points around the edge are the same distance from the center.
The diameter is the length of a straight line that goes through the center of a circle.
To find the diameter, multiply the radius by 2.
radius × 2 = diameter
The distance around a circle is called the circumference.
Think of it as the length of the line that goes around a circle.
Circles have a special property.
If you divide the circumference by the diameter of any circle, you get a special number called pi.
pi = 3.141592654...
The decimals in the value of pi just keep going on and on. It never ends, and the sequence of the digits never repeat.
Pi is a very important number. It helps us find the circumference of a circle.
Tip: you need to memorize at least the first 3 digits of pi, 3.14.
Pi ≈ 3.14
We use pi so much, it gets it own symbol.
The symbol for pi is this letter in the Greek alphabet: π.
To find the circumference, multiply pi with the diameter.
circumference = π × diameter
Wow, pi is super useful.
If you know the radius or diameter of a circle, you can use pi to figure out its circumference.
Excellent job learning about circles.
Now, complete the practice. It'll help you remember for longer.