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Section 10.3
Inscribed Angles
Inscribed Angle
• An angle whose vertex is on a circle and whose sides contain chords of the circle
Inscribed Angle
Intercepted Arc
• An arc formed from an inscribed angle on a circle.
Intercepted Arc
Measure of an Inscribed Angle
• Half the measure of its intercepted arc
D
A
B
m ADB = ½ m AB
OR
m AB = 2(mADB)50° 100°
Examples #1-6
Theorem 10.9
• If two inscribed angles of a circle intercept the same arc, then the angles are congruent.
A
CB
DC is congruent to D
It is given that mE 75.
What is the mF?
75
G
E
FH
mF = 75
Inscribed
• All of the vertices of a polygon lie on a circle
Circumsribed
• Surrounding the figure
Theorem 10.10
• If a right triangle is inscribed in a circle, then the hypotenuse is the diameter.
B is a right angle iff
AC is the diameter
A
B C
Theorem 10.11
• A quadrilateral can be inscribed in a circle iff its opposite angles are supplementary (180°)
GD
F
E
mD + mF 180
mE + mG 180
Examples #1-6