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G E O M E T R Y. 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.
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GEOMETRY Circle Terminology
Student Expectation 6th 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 • 7th Grade • 7.4.9AEstimate 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.
Circumference & Diameter The distance around a circle is called the circumference. The distance across a circle through the center is called the diameter.
The segment joining the center of a circle to a point on the circle. Example: OA Radius (or Radii for plural)
= Pi = 3.14 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.
Formulas Area & Circumferenceof a Circle Area = pi r 2 Circumference = Pi· d
Summary • 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