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Radii to Tangents - Concept 12,401 views

Teacher/Instructor Brian McCall
Brian McCall

Univ. of Wisconsin
J.D. Univ. of Wisconsin Law school

Brian was a geometry teacher through the Teach for America program and started the geometry program at his school

When a radius is drawn to a point of tangency, the angle formed is always a right (90 degree) angle. This fact is commonly applied in problems with two tangent segments drawn to a circle from a point. If two radii to tangents are drawn in, a kite with two right angles is formed and the missing angles or sides can be found. Related topics include central angles, tangent segments to a circle, and chords.

When we have a tangent to a circle which means it's a line or line segment or even a ray that intersects the circle on only one point if we had to draw a radius to that point, something special happens. Over here I've written a tangent to a circle is and I left it blank purposely perpendicular to the radius drawn at the point of tangency so I can label this as a 90 degree angle. You're going to apply this in lots of different problems where you see a tangent in some form being drawn where it's connected to a radius.