2. To denote the measure of an angle we write an
âmâ in front of the symbol for the angle.
Here are some common angles and their measurements.
2
1 2
3
4
1 45
mï ïœ ï° 2 90
mï ïœ ï°
3 135
mï ïœ ï°
4 180
mï ïœ ï°
Review
3. Congruent Angles
âą So, two angles are congruent if and only if they have the same
measure.
âą So, The angles below are congruent.
3
if and only if .
A B m A m B
ï ï ï ï ïœ ï
Means
Congruent
Means Equal
Review
4. Perpendicular Lines
âąTwo lines are perpendicular if they
intersect to form a right angle.
See the diagram.
âąSuppose 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.
âąSo, perpendicular lines intersect
to form four right angles.
4
1
2
3 4
5. Perpendicular Lines
âąThe symbol for perpendicularity is
âąSo, if lines m and n are perpendicular, then we write
.
ï
.
m n
ï
m
n
m n
ï
6. Adjacent Angles
Adjacent angles share a common vertex and one common side.
Adjacent angles are âside by sideâ
and share a common ray.
45Âș
15Âș
9. Vertical Angles
âąTwo angles formed by intersecting lines and have no
sides in common but share a common vertex.
âąAre congruent.
When 2 lines
intersect, they
make vertical
angles.
75Âș
75Âș
105Âș
105Âș
Commo
nVertex
15. Supplementary Angles
âą Two angles are supplementary if their measures add up to
âą If two angles are supplementary each angle is the supplement of
the other.
âą If two adjacent angles together form a straight angle as below,
then they are supplementary.
15
180 .
ï°
1 2
1 and 2 are
supplementary
ï ï
17. Complementary Angles
âą Two angles are if their measures add upcomplementary to
âą If two angles are complementary, then each angle is called the complement
of the other.
âą If two adjacent angles together form a right angle as below, then they are
complementary.
17
90 .
ï°
1
2
A
B
C
1 and 2 are
complementary
if is a
right angle
ABC
ï ï
ï
18. Supplementary vs.
Complementary
How do I remember?
The way I remember is this:
âą C comes before S in the alphabet.
âą 90 comes before 180 when I count.
âą Complementary is 90, Supplementary is 180.
24. GuessWho?
âą I am two adjacent angles.
âą I look like an âLâ with a line in the middle.
25. GuessWho?
âą I am two adjacent angles.
âą I look like an âLâ with a line in the middle.
⹠I add up to 90°
âą I look like this:
26. GuessWho?
âą I am two adjacent angles.
âą I look like an âLâ with a line in the middle.
⹠I add up to 90°
âą 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. SoâŠ..
180 â 120 = 60
The missing angle is 60
38. Find the missing angle
130
x
What kind of angles?
Whatâs the missing angle?
39. Find the missing angle
130 x
What kind of angles?
Supplementary
Whatâs the missing angle?
Adds up to 180, soâŠ..
180 â 130 = 50
71. ACTIVITY 1: LETâS PRACTICE!
Direction:WriteTrue if the statement is correct but if itâs 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.