Warm-upFind the measure of each arc.
Homework Review
EOCT Review
a) Centroid
b) Circumenter
c) Incenter
d) Orthocenter
b
A gazebo is to be constructed between three houses so that it will approximately be the same distance from each house. Which would be helpful in deciding where to locate the gazebo?
CCGPS GeometryDay 21 (9-5-13)
UNIT QUESTION: What special properties are found with the parts of a circle?Standard: MMC9-12.G.C.1-5,G.GMD.1-3
Today’s Question:How do we use angle measures to find measures of arcs?Standard: MMC9-12.G.C.2
Inscribed Angles
Inscribed Angle: An angle whose vertex is on the circle and whose sides are chords of the circle
INSCRIBEDANGLE
INTERCEPTED
ARC
Determine whether each angle is an inscribed angle. Name the intercepted arc for the angle.
C
LO
T1. YES
; CL
Determine whether each angle is an inscribed angle. Name the intercepted arc for the angle.
Q
R
K
V2. NO;
QVRS
2 ArcdIntercepteAngleInscribed
160
80
To find the measure of an inscribed angle…
120
x
What do we call this type of angle?What is the value of x?
y
What do we call this type of angle?How do we solve for y?The measure of the inscribed angle is HALF the
measure of the inscribed arc!!
Examples3. If m JK = 80, find m JMK.
M
Q
K
S
J
4. If m MKS = 56, find m MS.
40
112
72If two inscribed angles intercept the same arc, then they are congruent.
Example 5In J, m3 = 5x and m 4 = 2x + 9.Find the value of x.
3
QD
JT
U
4x = 3
If all the vertices of a polygon touch the edge of the circle, the polygon is INSCRIBED and the circle is CIRCUMSCRIBED.
2 Column Proof
A circle can be circumscribed around a quadrilateral if and only if its
opposite angles are supplementary.A B
CD
180 CmAm180 DmBm
z
y
110
85
110 + y =180y = 70
z + 85 = 180z = 95
Example 8 Find y and z.
180
diameter
If a right triangle is inscribed in a circle then the hypotenuse is the diameter of the circle.
HK
GN
4x – 14 = 90
Example 6In K, GH is a diameter and mGNH = 4x – 14. Find the value of x.
x = 26
HK
GN
6x – 5 + 3x – 4 = 90
Example 7In K, m1 = 6x – 5 and m2 = 3x – 4. Find the value of x.
x = 11
1
2
Homework:
• Worksheet