The Basics of a (Mathematical) Circle

The basic definition of a circle: A round two dimensional plane.

Diameter: The distance across a circle through its centre. (usually represented by d)

It is NOT this:

It is this:

Radius (Plural is Radii.): The distance from the centre of a circle to its outer edge (usually represented as r)

(Some random fact: If you measure from the centre to the outer edge of a "perfect" circle all around, the measurements will be virtually the same. This is what fully defines a circle, a round, two-dimensional plane that measured from the centre to the outer edge, the measurements would be equal in distance.)

We can now safely state that 2r=d. This means that 2 radii are needed to make the diameter of a circle.

Circumference: The perimeter around the circle, it is usually represented as C. (this is what I mean by "outer edge".)

To figure out the circumference, multiply the diameter by Pi (π).

Pi is approximate to 3.14.

Some circumference formulas:

C=πd

C=2πr

(I'll also throw in on how to figure out the area.)

Some equivalents to a rectangle or parallelogram:

Length/Height: Radius

Width/Base: Half of the circumference

How to figure out the area of a rectangle or parallelogram: Length x Width (or Base x Height)

Enough Parallelogram talk, to figure out the area of a circle is:

Pi radius square.