12.1 Tangent Lines

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12.1 Tangent Lines

• A tangent to a circle is a line in the plane of
  the circle that intersects the circle in exactly
  one point.
• The point where a circle and a tangent intersect
  is the point of tangency.

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Theorem 12.1

• If a line is tangent to a circle, then the line
  is perpendicular to the radius at the point of
  tangency.

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Finding Angle Measures

• Segment ML and segment MN are tangent to circle
  O. What is the value of x?
• LMNO is a quadrilateral.
• The sum of the angles is 360.
• 90 117 90 x 360
• 297 x 360
• x 63
• The measure of angle M is 63.

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Theorem 12.2

• If a line in the plane of a circle is
  perpendicular to a radius at its endpoint on the
  circle, then the line is tangent to the circle.

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Finding a Radius

• What is the radius of circle C?

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Identifying a Tangent

• Is segment ML tangent to circle N at L? Explain.

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Theorem 12.3

• If two tangent segments to a circle share a
  common endpoint outside the circle, then the two
  segments are congruent.

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More Practice!!!!!

• Homework Textbook p. 767 6 17.