Unit 8: Circle Geometry
Introduction ­ Terms
Diameter
the distance across a circle, measured through its center; or the line segment that joins two points on the circle and passes through the center.
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Radius
the distance or line segment from the center of a circle to any point on the circle
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Chord(s)
a line segment that joins two points on a circle
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A
B
Arc
a segment of the circumference of a circle
Minor Arc
the shorter of the two arcs between two points on a circle
For example
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Tangent
a line that intersects a circle at only one point
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Point of Tangency
the point where a tangent intersects a circle
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Central Angle
An angle whose arms are radii of a circle
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Q
P
R
Inscribed Angle
an angle in a circle with its vertex and endpoints of its arms on the circle
For example, click here for applet
Special properties to remember in this chapter
1) Sum of the angles in a triangle = 180 degrees
2) In an isosceles triangles base angle are equal
3) All radii in a circle are equal
4) In a right triangle you can find a missing side, if 2 are known, by using the Pythagorean theorem.
5) How to name an angle.
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AB is tangent and point O is the center of the circle.
Find the measure of angle ABC
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O is the center and CD is tangent to the circle. Find the length of the radius OC and then diameter of the circle.
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An airplane, A is cruising at an altitude of 9000m. A cross section of Earth is a circle with radius approximately 6400 km. A passenger wonders how far she is from a point H on the horizon she sees outside the window, Calculate the distance to the nearest KM.
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