The Geometry of a Circle
Lesson 19Topics
x Notation and jargon.
x The converse of Thales’s theorem.
x The tangent/radius theorem.
x The two tangents theorem.
x The inscribed/central angle theorem.
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x arc: For two given points on a circle, a section of the circumference of the circle between them is
called an arc of the circle. The measure of an arc is the measure of the angle between the two radii
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x chord: A line segment connecting two points on a circle.
x GLDPHWHU: A chord of a circle that passes through the center of the circle is called a diameter of
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x LQVFULEHGDQJOH: If P and Q are two endpoints of an arc of a circle and A is a point on the circle not on
the arc, then PAQ is an inscribed angle.
x radius: A line segment connecting the center of a circle to a point on the circle is called a radius of the
circle. The length of any such line segment is called the radius of the circle.
x VHFDQWWRDFLUFOH: A line that intercepts a circle at two distinct points.
x WDQJHQWWRDFLUFOH: A line that meets just one point of a circle.