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## Center of a Circle

• The center of a circle is the point within the circle equidistant from every point on the circle.

• The radius of a circle is the distance from the center of the circle and any point on the circle. The distance between the center and any point on the circle is always the same.

## Diameter of a Circle

• The diameter of a circle is any line that starts from one point on a circle, passes through the center of the circle, and ends at another point on the circle. The diameter of a circle is equal to twice the length of the radius of the circle.

## Chord of a Circle

• The chord of a circle is a line that starts at a point on a circle and ends on another point of a circle. The diameter of a circle is the longest chord of a circle.

## Circle Degrees

• There are 360 degrees in a circle. A semicircle, half of a circle, has 180 degrees. A quarter circle has 90 degrees. A portion of a circle is also referred to as a sector.

## Tangent and Secant of a Circle

• The tangent of a circle is a line that will intersect the circumference of a circle at one point. The tangent of a circle will always be perpendicular to the radius of a circle. The secant of a circle is a line that intersects a circle at two points. The difference between a chord of a circle and a secant of a circle is that the chord's endpoints are on the circumference of the circle.

## Circle Formulas and Applications

• The perimeter of a circle is called the circumference of the circle. The circumference is calculated by multiplying the number 3.14 by the diameter of the circle. The number 3.14 is called pi. The area of a circle is calculated by multiplying the number pi by the radius squared. The area of a circle is used to determine the volume of a cylinder. The area of a cylinder's circular surface is multiplied by the height of the cylinder to determine its volume.

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