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Lines and Angles
PARALLEL LINES
• Def: line that do not intersect.
B
• Illustration:
A
l
m
• Notation:
D
C
l || m
AB || CD
Examples of Parallel Lines
•
•
•
•
•
Hardwood Floor
Opposite sides of windows, desks, etc.
Parking slots in parking lot
Parallel Parking
Streets: Laramie & LeClaire
PERPENDICULAR LINES
• Def: Lines that intersect to form a right angle.
m
• Illustration:
n
• Notation: m  n
• Key Fact: 4 right angles are formed.
Ex. of Perpendicular Lines
• Window panes
• Streets: Belmont and Cicero
Angles
Two rays or line segments that meet at a point form an angle.
The point where the rays meet is called the vertex of the
angle.
We measure the size of an angle using degrees.
Two ways to label angles:
1. by giving the angle a name, usually a lower-case letter
like a or b, or sometimes a Greek letter like α (alpha) or θ
(theta), or sometimes a number
2. or by the three letters on the shape that define the angle,
with the middle letter being the vertex.
Example angle "a" is "BAC” (or
“CAB”),
and angle "θ" is "BCD” (or “DCB”)
Measuring Angles
• This is one degree:
• A Full Circle is 360°
• Half a circle is 180°
(called a straight angle)
• Quarter of a circle is 90°
(called a right angle)
Types of Angles
Angle Names:
Acute – less than 90 degrees
Right – exactly 90 degrees (indicated on the GED by a square in the
corner of the angle)
Obtuse – more than 90 degrees
Straight – exactly 180 degrees
Complementary Angles
Two angles are called complementary angles if the sum of their
degree measurements equals 90 degrees.
One of the complementary angles is said to be the complement
of the other.
• Supplementary angles add up to 180 degrees
Vertical Angles
Two straight lines crossing create vertical angles. Vertical angles
(such as <BEC and <AED) have equal angle measurements.
In the diagram below, <AEB and <DEC are also vertical and
therefore equal angles.
Corresponding Angles
• A line going through two parallel lines creates corresponding
angles.
• Corresponding angles (such as <D and <B) have equal
measurements.
• In the diagram below, <C and <A are also corresponding and
therefore equal angles.
Corresponding
5
4
6
3
7
2
1
8
t
Corresponding
4 and 2
3 and 1
5 and 7
6 and 8
5
4
6
3
7
2
1
8
t
Angle Measurements
• If <VNL measures 130°, what is the
measurement of <UNB?
Angle Measurements
• If <VNL measures 130°, what is the
measurement of <UNB?
• <VNL and <UNB are
vertical angles. Therefore,
their measurements are the same.
<UNB = 130°
Angle Measurements
• If <VNL measures 130°, what is the
measurement of <LNB?
Angle Measurements
• If <VNL measures 130°, what is the
measurement of <LNB?
• <VNL and <LNB are supplementary angles.
• 180 – 130 = 50
• <LNB = 50°
Angle Measurements
• If <SMP is a right angle and <ZMP measures
43°, what is the measurement of <ZMS?
Angle Measurements
• If <SMP is a right angle and <ZMP measures
43°, what is the measurement of <ZMS?
• <ZMP and <ZMS are
complementary angles.
90 – 43 = 47
<ZMS = 47°
Angle Measurements
• <QFL is a straight angle. If <LFC measures 50°,
what is the measurement of <QFC?
Angle Measurements
• <QFL is a straight angle. If <LFC measures 50°,
what is the measurement of <QFC?
• The angles are supplementary
• 180 – 50 = 130
• <QFC = 130°
Angle Measurements
• If <AKS is 38°, find the measurements of all of
the other angles
If <AKS is 38°, find the measurements of all of the other angles
• <EKR is vertical to <AKS,
so <EKR = 38°
• <AKE is supplementary to
<EKR, so <AKE = 142° (180 – 38)
• <RKQ is complementary to <EKR, so <RKQ = 52° (90 – 38)
• Finally, <SKQ is supplementary to <EKQ, so it must measure
90° (180 – 90)
Angle Measurements
• If <NTF measures 125°, what are the
measurements of the other angles?
If <NTF measures 125°, what are the measurements of the other angles?
• <NTF is supplementary to <RTN,
so <RTN must be 55° (180 – 125)
• <FTY is vertical to <RTN and supplementary
to <NTF, so it must also be 55°
• <RTY is vertical to NTF and supplementary to <FTY, so it must
also measure 125°
• <NTF corresponds with <KRT, so they have
the same measurements. <KRT = 125°
• <TRU = 55° (corresponding to <FTY)
• <XRU = 125° (corresponding to <RTY)
• <XRK = 55° (corresponding to <RTN)
• WHEW!
• All the interior angles of any triangle will
together add up to 180°
• All the interior angles of any quadrilateral
(square, rectangle, parallelogram, trapezoid)
will add up to 360°
• What is the measure of the missing angle,
<BAC?
• What is the measure of the missing angle,
<BAC?
All triangles have interior angles totaling 180°,
So 180 – (52 + 48) gives us:
<BAC = 80°
• Find the measure of the missing angle:
• Find the measure of the missing angle:
• All quadrilaterals have
interior angles totaling 360°,
so, 360 – (68+106+126)
360 – 300 = 60
gives us:
angle x measures 60°
Lines and Angles
• Pages 167 – 170 in the book
– Check answers online
• Pages 29-30 in the GED Practice Packet
– Enter answers online