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WARM UP
How many sides are there in a
Triangle ____________
three
four
Quadrilateral ___________
Pentagon _____________
five
A right angle is _____°
90
An acute angle is an angle which is
______
less than 90°
An obtuse angle is an angle which
greater /
is ____________
than 90°
more
A right angle is _____°
90
An acute angle is an angle which is
______
less than 90°
An obtuse angle is an angle which
greater /
is ____________
than 90°
more
ANGLE PROPERTIES
When two straight lines cross, the
angles formed on either side are
called opposite angles
Opposite angles are equal
a
Angles along a straight line are called
supplementary angles.
Supplementary angles add to 180°
a
Angles dividing a right angle are
called complementary angles
Complementary angles add to 90°
b
b
a=b
a+b=
180°
a + b = 90°
a
b
ANGLE PROPERTIES
EXAMPLE
When two straight lines
cross, the angles formed on
either side are called
opposite angles
Opposite angles are equal
Calculate the measure of the unknown
angle
Angles along a straight line
are called supplementary
angles.
Supplementary angles add
to 180°
Angles dividing a right angle
are called complementary
angles Complementary
angles add to 90°
(a)
a
73°
a = 73°
(b)
b + 123° = 180°
123°
b
b = 180° - 123°
b = 57°
ANGLE PROPERTIES
EXAMPLE
When two straight lines
cross, the angles formed on
either side are called
opposite angles
Opposite angles are equal
Calculate the measure of the unknown
angle
(c)
a
Angles along a straight line
are called supplementary
angles.
Supplementary angles add
to 180°
43°
a + 43° = 90°
a = 90° - 43°
Angles dividing a right angle
are called complementary
angles Complementary
angles add to 90°
a = 47°
ANGLE PROPERTIES
When two straight lines
cross, the angles formed on
either side are called
opposite angles
Opposite angles are equal
Angles along a straight line
are called supplementary
angles.
Supplementary angles add
to 180°
Angles dividing a right angle
are called complementary
angles Complementary
angles add to 90°
The angle with the dot is XYZ
NAMING ANGLES and SIDES
To identify angles in polygons or
angles involving parallel lines (lines
that never meet), you may need to use
three letters.
X
Y
Z
EXAMPLE
The right angle pictured below is
labelled as ABC
A
A side of a triangle or polygon can be
identified by the two vertices on the
ends of the line segment.
EXAMPLE
The side labelled x can be expressed
B
as side AB
x
B
C
C
A
NAMING ANGLES and SIDES
1. Use three letters to name the angle with the dot in each diagram
B
(a)
(b)
C
A
B
C
A
BCA
BCD
D
NAMING ANGLES and SIDES
2. For each diagram, use two letters to identify the side marked with the x
(a)
(b)
D
J
I
x
x
K
E
F
DF
H
JK