Circles

Diameter is the distance across a circle through its centre

Some Examples:

Radius (radii is the plural) is the distance from the centre of a circle to its outer edge

Some Examples:

We can do the formula 2R=D this means that 2 radii are needed to make a diameter of a circle.
1/2 x D = R
D/2 = R
Example:











Here's a video....




This has some extra things but it's still helpful.




More Help? Then Check this out. (it has some extra stuff but it still helps)