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Circle Anatomy and Core Attributes
Answer Key
Circle Anatomy and Core Attributes Answer Key
Worksheet 1 of 5 in the Grade 7 circles series. Name the parts of a circle and move between radius and diameter. Next: The Meaning of Pi.
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Lesson Notes
A circle is the set of all points that are the same distance from one fixed point, the center. Every other part of a circle is named by how it relates to the center.
Key vocabulary
- Radius ($r$): a segment from the center to any point on the circle. Every radius of a circle is the same length.
- Diameter ($d$): a segment from one point on the circle to another that passes through the center. It is the longest segment (chord) you can draw inside a circle.
- Chord: any segment with both endpoints on the circle. A diameter is a special chord.
- Circumference ($C$): the distance around the circle (its perimeter). You will use it in the next worksheets.
The one relationship to memorize
$d = 2r$$r = d \div 2$
If you know one, you can always find the other. Doubling the radius gives the diameter; halving the diameter gives the radius.
Worked example
A circle has a diameter of 15 cm. Find the radius.
$r = d \div 2 = 15 \div 2 = 7.5$ cm
Watch for the words. "Across," "from edge to edge," and "the widest part" all describe a diameter. "From the center," "spray distance," and "rope length" all describe a radius.
25 problems. Show your work in the space under each problem, then put a box around your answer. No $\pi$ is needed on this worksheet. On screen, the eye at the right of each problem shows or hides the worked solution.