1.5 Angle Bisectors
Angle Bisector
• A ray that divides an angle into 2 congruent
adjacent angles.
A
D
B
C
BD is an angle
bisector of <ABC.
Ex1: If FH bisects EFG &
mEFG=80o, what is mEFH?
E
H
F
80
 40 o
2
m  EFH  40
o
G
#2 you try: If FH bisects EFG &
mEFG=130o, what is mEFH?
H
E
F
G
130
 65 o
2

m  EFH  65
EX #3!!: Find mCBD
* If they are
congruent, set them
equal to each other,
then solve!
C
A
x+40 = 3x-20
D
B
40 = 2x-20
60 = 2x
3x-20o =
3(30)-20 =
70o
30 = x
#4 you try!!: Find mABD
* If they are
congruent, set them
equal to each other,
then solve!
C
A
x+40 = 3x-20
D
B
3x-20o
=
3(30)-20 =
Since both angles are
congruent,
70o +70o
70o
=140º
40 = 2x-20
60 = 2x
30 = x
CONSTRUCTION OF AN
ANGLE BISECTOR
• http://www.mathopenref.com/constbisec
tangle.html
ANGLE BISECTOR
PRACTICE
• USING A COMPASS & RULER,
CONSTRUCT THE ANGLE BISECTOR
FOR EACH PROBLEM ON THE
WORKSHEET BEING PASSED OUT.
• COMPARE ANSWERS WITH YOUR
NEIGHBOR.