9.8. Angles Outside a Circle http://www.ck12.org
x=^120
◦− 32 ◦
2 =
88 ◦
2 =^44◦.
Example C
Find the value ofx.
First note that the missing arc by anglexmeasures 32◦because the complete circle must make 360◦. Then,x=
141 ◦− 32 ◦
2 =
109 ◦
2 =^54.^5◦.
Watch this video for help with the Examples above.
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/52417CK-12 Foundation: Chapter9AnglesOutsideaCircleB
Concept Problem Revisited
If 178◦of the Earth is exposed to the sun, then the angle at which the sun’s rays hit the Earth is 2◦. From the Outside
Angle Theorem, these two angles are supplementary. From this, we also know that the other 182◦of the Earth is not
exposed to sunlight and it is probably night time.
Vocabulary
Acircleis the set of all points that are the same distance away from a specific point, called thecenter. Aradiusis
the distance from the center to the circle. Achordis a line segment whose endpoints are on a circle. Adiameteris
a chord that passes through the center of the circle. The length of a diameter is two times the length of a radius. A