# GEOMETRYGEOMETRY Circle Terminology. Student Expectation 6 th Grade: 6.3.6C Describe the relationship between radius, diameter, and circumference of a.

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GEOMETRYGEOMETRY Circle Terminology

Student Expectation 6 th Grade: 6.3.6C Describe the relationship between radius, diameter, and circumference of a circle. 6.4.8A Estimate measurements (including circumference) and evaluate reasonableness of results.

Student Expectation 7 th Grade 7.4.9A Estimate measurements and solve application problems involving length (including perimeter and circumference) and area of polygons and other shapes.

Circle A circle is a shape with all points the same distance from the center. It is named by the center. The circle at the bottom is called circle A since the center is at point A.

The distance around a circle is called the circumference. The distance across a circle through the center is called the diameter. Circumference & Diameter

Radius (or Radii for plural) The segment joining the center of a circle to a point on the circle. Example: OA

Pi is the ratio of the circumference of a circle to the diameter. Thus, for any circle, if you divide the circumference by the diameter, you get a value close to Pi. The value of Pi is approximately 3.14. = Pi = 3.14

Formulas Area & Circumference of a Circle Area = pi r 2 Circumference = Pi · d

The number Pi is the ratio of the circumference of a circle to the diameter. The value of Pi is approximately 3.14. The diameter of a circle is twice the radius. Given the diameter or radius of a circle, we can find the circumference. We can also find the diameter (and radius) of a circle given the circumference. The formula for diameter is d = 2 · r The formula for circumference is C = Pi · d Summary