Students learn the following theorems related to tangents. If a line is tangent to a circle, then the line is perpendicular to the radius at the point of tangency. If a line is perpendicular to a radius at its outer endpoint, then the line is tangent... to the circle. If two tangent segments are drawn to a circle from an external point, then the tangent segments are congruent. Students are then asked to use these theorems to find missing segment lengths and missing angle measures in given figures. Students also learn the definitions of common internal tangents and common external tangents. (03:07)[more]

Students learn the definitions of a circle (is a set of points in a plane that are a given distance from a given point in the plane), the given point is called the center, and the distance from the center to the circle is called the radius. Whicheve...r point on the circle is chosen the distance to the center of the circle will be the same, so all radii of a given circle are congruent. Good quality video for grade four and up. (01:53)[more]

Students learn the definitions of a circle (is a set of points in a plane that are a given distance from a given point in the plane), the given point is called the center, and the distance from the center to the circle is called the radius. Whicheve...r point on the circle is chosen the distance to the center of the circle will be the same, so all radii of a given circle are congruent. Good quality video for grade four and up. (01:06)[more]

This video explains finding circumference by using radius. A "real-life" example of finding circumfernce of a traffic circle is shown with video and explained. ( 2:42)

From gamequarium.org, produced by Learning Upgrade

A musical presentation that explains that a circle is a shape where the diameter is twice the radius. This two-minute video explains the various formulas. Students should enjoy it. (01:52)

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