What does a circle and rotational symmetry have in common? A circle has 360 degrees. In order to determine if a polygon has rotational symmetry, we need to rotate it in a circular motion. If we rotate that polygon less than 360 degrees and it fits on top of its original position, then it has rotational symmetry.
We used this knowledge to understand, interpret and create circle graphs. Circle graph is just like a pie chart. If we collect data from 24 people, then each part of the circle should add up to 24. The data collected represents a portion of the circle (or pie). If the total number of data collected is 24, then 12 represents half (or 50%) of the circle. So, half or 50% of the people chose blue as their favorite color. 4 out of 24 people chose yellow. This number represents 1/6 of the total number of people, so it should occupy 1/6 of the circle. 8 people chose red, which represents 1/3 of the total number of people, so it should occupy 1/3 of the circle.
If we divide the circle into 12 equal sections (similar to a clock), then each section of the circle will represent 2 people because 24 divided by 12 equals 2.
Why do students need to know or be able to do this?
- Students apply their discoveries about angles in a circle to interpret and create circle graphs.
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