eBook
Mathigon

Mathigon: Geometry: Circle and Pi: Degrees and Radians

For Students 9th - 10th Standards
Rather than dividing a circle into some number of segments (like 360 degrees), mathematicians often prefer to measure angles using the circumference of a unit circle - a circle with radius 1. This way of measuring angles is called...
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Khan Academy

Khan Academy: Points Inside/outside/on a Circle

For Students 9th - 10th
Given the center and radius of a circle, determine if a point is inside of the circle, on the circle, or outside of the circle.
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Co Seven Circles Ii

For Teachers 9th - 10th Standards
In this task, seven pennies are placed in a circle so that they are all touching one in the center and their neighbors. Students are asked to find as many rigid motions of the plane as they can which are symmetries of this configuration...
Lesson Plan
Illustrative Mathematics

Illustrative Mathematics: G Gpe, F Tf Coordinates of Points on a Circle

For Teachers 9th - 10th Standards
For this task, students are shown a unit circle in a plane and an angle measured from the x-axis. They must determine the coordinates of the line segment for the angle and answer a question about the sum of the coordinates. The purpose...