## You Can attract It Yourself

Put a pin in a board, placed a loop that string around it, and insert a pencil right into the loop. Keep the cable stretched and also draw the circle!

## Play through It

Try dragging the suggest to see just how the radius and also circumference change.

You are watching: A portion of the circumference of a circle

(See if you deserve to keep a consistent radius!)

## Radius, Diameter and Circumference

The Radius is the street from the center outwards.

The **Diameter** goes straight across the circle, through the center.

The **Circumference** is the distance once around the circle.

And right here is the really cool thing:

So as soon as the diameter is 1, the one is 3.141592654... |

We can say:

Circumference = π × Diameter

### Example: girlfriend walk about a circle which has a diameter that 100m, how far have girlfriend walked?

Distance to walk = circumference = π × 100m

= **314m** (to the nearest m)

Also note that the Diameter is double the Radius:

Diameter = 2 × Radius

And so this is likewise true:

Circumference = 2 × **π** × Radius

In Summary:

× 2 | × π |

Radius | Diameter | Circumference |

## Remembering

The size of the native may help you remember:

**Radius**is the shortest word and also shortest measure

**Diameter**is longer

**Circumference**is the longest

## Definition

The one is a plane shape (two dimensional), so: |

## Area

The area that a one is **π** time the radius squared, which is written:

A = **π** r2

Where

**A**is the Area

**r**is the radius

To help you mental think "Pie room Squared" (even despite pies room usually round):

Or, making use of the Diameter:

A = (**π**/4) × D2

### Area compared to a Square

A circle has **about 80%** of the area the a similar-width square.**The actual value is (π/4) = 0.785398... = 78.5398...%**

**And something amazing for you:**

**See circle Area through Lines**

**Names**

**Because civilization have studied circles for countless years unique names have actually come about.**

**Nobody wants to to speak "that line that starts at one next of the circle, goes v the center and ends ~ above the various other side" once they can just to speak "Diameter".**

**So right here are the most common special names:**

**Lines**

**A line the "just touches" the circle as it overcome by is called a Tangent**.

A line that cut the one at two points is dubbed a **Secant**.

A heat segment the goes from one allude to one more on the circle"s one is referred to as a **Chord**.

If that passes with the facility it is dubbed a **Diameter**.

And a component of the circumference is called an **Arc**.

## Slices

There are two main "slices" the a circle.

The "pizza" slice is dubbed a Sector.

And the slice made by a chord is called a Segment.

## Common Sectors

The Quadrant and Semicircle space two special species of Sector:

Quarter that a one is called a **Quadrant**.

Half a one is referred to as a **Semicircle.**

## Inside and also Outside

A circle has an inside and also an exterior (of course!). Yet it likewise has an "on", because we could be appropriate on the circle.

Example: "A" is external the circle, "B" is within the circle and also "C" is top top the circle.

See more: Vòng Tay Lu Thống Cẩm Thạch, Ý Nghĩa Lu Thống Phong Thủy Là Gì

### Ellipse

A circle is a "special case" of one ellipse.

Activity: Approximate value For Pi

Pi airplane Unit circle Circle Sector and Segment one Equations plane Geometry Geometry table of contents