2. To denote the measure of an angle we write an
“m” in front of the symbol for the angle.
Here are some common angles and their measurements.
2
1 2
3
4
1 45
m 2 90
m
3 135
m
4 180
m
Review
3. Congruent Angles
• So, two angles are congruent if and only if they have the same
measure.
• So, The angles below are congruent.
3
if and only if .
A B m A m B
Means
Congruent
Means Equal
Review
4. Perpendicular Lines
•Two lines are perpendicular if they
intersect to form a right angle.
See the diagram.
•Suppose angle 2 is the right angle.
Then since angles 1 and 2 are
supplementary, angle 1 is a right
angle too. Similarly, angles 3 and
4 are right angles.
•So, perpendicular lines intersect
to form four right angles.
4
1
2
3 4
5. Perpendicular Lines
•The symbol for perpendicularity is
•So, if lines m and n are perpendicular, then we write
.
.
m n
m
n
m n
6. Adjacent Angles
Adjacent angles share a common vertex and one common side.
Adjacent angles are “side by side”
and share a common ray.
45º
15º
9. Vertical Angles
•Two angles formed by intersecting lines and have no
sides in common but share a common vertex.
•Are congruent.
When 2 lines
intersect, they
make vertical
angles.
75º
75º
105º
105º
Commo
nVertex
15. Supplementary Angles
• Two angles are supplementary if their measures add up to
• If two angles are supplementary each angle is the supplement of
the other.
• If two adjacent angles together form a straight angle as below,
then they are supplementary.
15
180 .
1 2
1 and 2 are
supplementary
17. Complementary Angles
• Two angles are if their measures add upcomplementary to
• If two angles are complementary, then each angle is called the complement
of the other.
• If two adjacent angles together form a right angle as below, then they are
complementary.
17
90 .
1
2
A
B
C
1 and 2 are
complementary
if is a
right angle
ABC
18. Supplementary vs.
Complementary
How do I remember?
The way I remember is this:
• C comes before S in the alphabet.
• 90 comes before 180 when I count.
• Complementary is 90, Supplementary is 180.
24. GuessWho?
• I am two adjacent angles.
• I look like an “L” with a line in the middle.
25. GuessWho?
• I am two adjacent angles.
• I look like an “L” with a line in the middle.
• I add up to 90°
• I look like this:
26. GuessWho?
• I am two adjacent angles.
• I look like an “L” with a line in the middle.
• I add up to 90°
• I look like this:
Complementary Supplementary
37. Find the missing angle
120
x
I know these are supplementary angles.
Supplementary angles add up to 180.
The given angle is 120. So…..
180 – 120 = 60
The missing angle is 60
38. Find the missing angle
130
x
What kind of angles?
What’s the missing angle?
39. Find the missing angle
130 x
What kind of angles?
Supplementary
What’s the missing angle?
Adds up to 180, so…..
180 – 130 = 50
71. ACTIVITY 1: LET’S PRACTICE!
Direction:WriteTrue if the statement is correct but if it’s False,
change the
underlined word or number to make the whole statement true.
__________1.Complementary angles measure 180 degree.
__________2.The sum of the measures of angles at a point is 360
degree.
__________3. If two angles form a linear pair, then they are
complementary.
__________4.The measures of adjacent angles are congruent.
__________5. If the sum of two adjacent angles is 180degree, then
these angles form a linear pair.
72.
73.
74. Valuing
REFLECTION: (JournalWriting)
Take a look around you.There are many things
that works in pair. Give one example of it and
compose a song pertaining to the importance of
working by pair in real life.