The number of square units it takes to completely fill an
annulus.

Try this Drag the orange dots to move and resize the circles. As the size of the circles
change, the area is recalculated.

R | is the radius of the outer circle |

H | is the radius of the inner 'hole' |

π | is Pi, approximately 3.142 |

This simplifies a little to:

- In the figure above, click on "hide details"
- Drag the orange dots on the edge of the circles to make a random-size annulus.
- Now try to estimate the area of the annulus just by looking at the squares inside it
- Calculate the area using the formula

- Circle definition
- Radius of a circle
- Diameter of a circle
- Circumference of a circle
- Parts of a circle (diagram)
- Semicircle definition
- Tangent
- Secant
- Chord
- Intersecting chords theorem
- Intersecting secant lengths theorem
- Intersecting secant angles theorem
- Area of a circle
- Concentric circles
- Annulus
- Area of an annulus
- Sector of a circle
- Area of a circle sector
- Segment of a circle
- Area of a circle segment (given central angle)
- Area of a circle segment (given segment height)

- Basic Equation of a Circle (Center at origin)
- General Equation of a Circle (Center anywhere)
- Parametric Equation of a Circle

- Arc
- Arc length
- Arc angle measure
- Adjacent arcs
- Major/minor arcs
- Intercepted Arc
- Sector of a circle
- Radius of an arc or segment, given height/width
- Sagitta - height of an arc or segment

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