1. Angle Interior Any points that lie inside the rays of an angle. G B CJ H
Examples:
Point B is in the interior of ÐGHC
Point D is in the interior of ÐGHJ and ÐCHJ
Point A is NOT in the interior of ÐGHJ B C D A

2. Classifying Angles Acute Obtuse Right Straight
An angle that measures between 0 and 90 degrees.
Example: ÐABC is an acute angle.
mÐABC = 30. A B C
30°
Obtuse
An angle that measures between 90 and 180 degrees.
Example: ÐDEF is an obtuse angle.
mÐDEF = 110. D E F
110°
Right
An angle that measures exactly 90 degrees.
Example: ÐGHJ is a right angle. mÐGHJ = 90. G H J
90°
Straight
An angle that measures exactly 180 degrees.
Example: ÐKLM is a straight angle.
mÐKLM = 180. K L M
180°
A right angle in a diagram is denoted by a square in the corner of the angle.

3. Classifying Angles An angle that measures between 0 and 90 degrees.
Example: ÐABC is an acute angle.
mÐABC = 30. A B C
30°
An angle that measures between 90 and 180 degrees.
Example: ÐDEF is an obtuse angle.
mÐDEF = 110. D E F
110°
An angle that measures exactly 90 degrees.
Example: ÐGHJ is a right angle. mÐGHJ = 90. G H J
90°
An angle that measures exactly 180 degrees.
Example: ÐKLM is a straight angle.
mÐKLM = 180. K L M
180°
A right angle in a diagram is denoted by a square in the corner of the angle.

4. Congruent Angles Congruent Angles – angles that have equal measures.
Recall the Definition of Congruent: Figures that are the same shape and size.
Congruent Angles – angles that have equal measures.
Notation:
ÐZIP M A T Z I P
120°
mÐMAT = mÐZIP

5. Adjacent Angles C B T A ÐCAB and ÐBAT are adjacent angles.
Two angles that…
1) Share a side.
2) Share their vertex.
3) Do not overlap (share any interior points). C T B A
ÐCAB and ÐBAT are adjacent angles.
ÐCAT and ÐBAT are NOT adjacent because they share interior points (overlap).

6. Angle Bisector
a ray that divides an angle into two congruent adjacent angles.
WY is the angle bisector of ÐXWZ.
and therefore,
ÐYWZ Y X
60° Z W

7. Complementary & Adjacent Angles
Complementary Angles
two angles whose measures sum to 90°.
35°
55°
20°
70°
Complementary Angles
Complementary & Adjacent Angles

8. Supplementary & Adjacent Angles
Supplementary Angles
two angles whose measures sum to 180°.
110°
70°
125°
55°
Supplementary Angles
Supplementary & Adjacent Angles

9. Linear Pair = A Pair of Angles that forms a Line.
two supplementary, adjacent angles.
120°
60°
Linear Pair = A Pair of Angles that forms a Line.

10. Vertical Angles – always congruent!
When two lines intersect, they form two pairs of vertical angles. The vertical angle pairs are the non-adjacent angles. 1 2 3 4
Ð1 and Ð2 are vertical angles.
Ð3 and Ð4 are vertical angles.