lesson 3-1
DESCRIPTION
Triangle Fundamentals. Lesson 3-1. Polygon. Polygon - closed figure, in a plane (2-D), made of segments intersecting only at their endpoints. EX). NOT EX). Triangles. 3. Triangle - sided polygon- ABC. Vertices-. Sides of a -. A. A B C. AB BC AC. B. C. B. C. A. - PowerPoint PPT PresentationTRANSCRIPT
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Lesson 3-1: Triangle Fundamentals
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Lesson 3-1
Triangle Fundamentals
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Polygon
Lesson 3-1: Triangle Fundamentals
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Polygon - closed figure, in a plane (2-D), made of segments intersecting only at their endpoints
EX)
NOT EX)
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Triangles Triangle- sided polygon- ABC
Lesson 3-1: Triangle Fundamentals
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3
Sides of a -
ABBCAC
Vertices-
ABC
A
B C
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Lesson 3-1: Triangle Fundamentals
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Naming Triangles
For example, we can call the following triangle:
Triangles are named by using its vertices.
∆ABC ∆BAC
∆CAB ∆CBA∆BCA
∆ACB
A
B
C
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Lesson 3-1: Triangle Fundamentals
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Opposite Sides and Angles
A
B C
Opposite Sides:
Side opposite to A :
Side opposite to B :
Side opposite to C :
Opposite Angles:
Angle opposite to : A
Angle opposite to : B
Angle opposite to : C
BC
AC
AB
BC
AC
AB
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Lesson 3-1: Triangle Fundamentals
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Classifying Triangles by Angles
Acute:
Obtuse:
A triangle in which all angles are less than 90˚.
A triangle in which and only angle is greater than 90˚& less than 180˚
100
45
35 B
C
A
50 60
70
G
H I
3
1 1
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Lesson 3-1: Triangle Fundamentals
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Classifying Triangles by Angles
Right:
Equiangular:
A triangle in which and only angle is 90˚
A triangle in which all angles are the same measure.
34
56
90B C
A
60
6060C
B
A
1 1
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Lesson 3-1: Triangle Fundamentals
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Classifying Triangles by Sides
Equilateral:
Scalene:No 2 sides are congruent
A triangle in which all 3 sides are different lengths.
Isosceles: A triangle in which at least 2 sides are equal.
A triangle in which all 3 sides are equal.
AB
= 3
.02
cm
AC
= 3.15 cm
BC = 3.55 cm
A
B CAB =
3.47
cmAC = 3.47 cm
BC = 5.16 cmBC
A
HI = 3.70 cm
G
H I
GH = 3.70 cm
GI = 3.70 cm
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Lesson 3-1: Triangle Fundamentals
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polygons
Classification by Sides with Flow Charts & Venn Diagrams
triangles
Scalene
Equilateral
Isosceles
Triangle
Polygon
scalene
isosceles
equilateral
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Lesson 3-1: Triangle Fundamentals
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polygons
Classification by Angles with Flow Charts & Venn Diagrams
triangles
Right
Equiangular
Acute
Triangle
Polygon
right
acute
equiangular
Obtuse
obtuse
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Parts of a right
Lesson 3-1: Triangle Fundamentals
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LEG
LEG
HYPOTENUSE
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Parts of an Isoceles
Lesson 3-1: Triangle Fundamentals
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A
B C
LEG LEG
BASE
Base Angles
Vertex AngleThe congruent sides are called legs and the third side is called the base
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Lesson 3-1: Triangle Fundamentals
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Theorems & Corollaries
The sum of the interior angles in a triangle is 180˚.
Angle Sum Theorem:
Third Angle Theorem:If two angles of one triangle are congruent to two angles of a second triangle, then the third angles of the triangles are congruent.
Corollary 1: Each angle in an equiangular triangle is 60˚.
Corollary 2: Acute angles in a right triangle are complementary.
Corollary 3: There can be at most one right or obtuse angle in a triangle.
Auxillary Line: A line added to a picture to help prove something
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Lesson 3-2: Isosceles Triangle 14
Isosceles Triangle Theorems
By the Isosceles Triangle Theorem,the third angle must also be x.Therefore, x + x + 50 = 180
2x + 50 = 1802x = 130x = 65
Example:
x
50
Find the value of x.
A
B C
, .If AB AC then B C
If two sides of a triangle are congruent, then the angles opposite those sides are congruent.
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Lesson 3-2: Isosceles Triangle 15
Isosceles Triangle TheoremsIf two angles of a triangle are congruent, then the sides opposite those angles are congruent.
Example: Find the value of x. Since two angles are congruent, the sides opposite these angles must be congruent.
3x – 7 = x + 152x = 22X = 11
A
B C
50 50
3x - 7x+15
A
B C
, .If B C then AB AC
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Lesson 3-1: Triangle Fundamentals
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Exterior Angle Theorem
The measure of the exterior angle of a triangle is equal to the sum of the measures of the remote interior angles.
Exterior AngleRemote Interior Angles A
BC
D
m ACD m A m B
Example:
(3x-22)x80
B
A DC
Find the mA.
3x - 22 = x + 80
3x – x = 80 + 22
2x = 102
mA = x = 51°
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Lesson 4-2: Congruent Triangles 17
Lesson 4-2
Congruent Triangles
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Lesson 4-2: Congruent Triangles 18
Congruent Figures
Congruent figures are two figures that have the same size and shape.
IF two figures are congruent THEN they have the same size and shape.
IF two figures have the same size and shape THEN they are congruent.
Two figures have the same size and shape IFF they are congruent.
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Congruent Triangles
Lesson 4-2: Congruent Triangles 19
ZY
MN ___
NR ___
MR ___
N
M
R
F E
D
≡ ≡=
=
│ │
∆MNR ______
M ____ D
N _____
R ______
E
F
∆ DEF
∆MNR ∆FED
Note:DE
EFDF
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Lesson 4-2: Congruent Triangles 20
Congruent Triangles - CPCTC
If ABC PQR
CPCTC: Corresponding Parts of Congruent Triangles are Congruent
Two triangles are congruent IFF their corresponding parts (angles and sides) are congruent.
BC
A
QR
PA ↔ P; B ↔ Q; C ↔ R
Vertices of the 2 triangles correspond in the same order as the triangles are named.
Corresponding sides and angles of the two congruent triangles:
A
A P B Q C
B PQ BC Q C P
R
R A R
≡
≡
=
=
│
│
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Lesson 4-2: Congruent Triangles 21
When referring to congruent triangles (or polygons), we must name corresponding vertices in the same order.
R
AY
S
UN
S
U
N
R
A
YSUN RAY
Also NUS YAR
Also USN ARY
Example…………
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Lesson 4-2: Congruent Triangles 22
Example ………
M
O
N
TA SR
UP
E
1. Pentagon MONTA Pentagon PERSU
2. Pentagon ATNOM Pentagon USREP
3. Etc.
If these polygons are congruent, how do you name them ?
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Lesson 4-3: SSS, SAS, ASA 23
Included Angles & Sides
& .A is the included angle for AB AC
& .B is the included angle for BA BC
& .C is the included angle for CA CB
A
B C
Included Angle:
Included Side:& .AB is the included side for A B
& .BC is the included side for B C
& .AC is the included side for A C
** *
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Lesson 4-3: SSS, SAS, ASA 24
Lesson 4-3
Proving Triangles Congruent(SSS, SAS, ASA)
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Lesson 4-3: SSS, SAS, ASA 25
PostulatesASA If two angles and the included side of one triangle are
congruent to the two angles and the included side of another triangle, then the triangles are congruent.
SAS If two sides and the included angle of one triangle are congruent to the two sides and the included angle of another triangle, then the triangles are congruent.
A
B C
D
E F
A
B C
D
E F
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Lesson 4-3: SSS, SAS, ASA 26
PostulatesSSS If the sides of one triangle are congruent to the sides of a
second triangle, then the triangles are congruent.
Included Angle: In a triangle, the angle formed by two sides is the included angle for the two sides.
Included Side: The side of a triangle that forms a side of two given angles.
A
B C
D
E F
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Lesson 4-3: SSS, SAS, ASA 27
Steps for Proving Triangles Congruent
1. Mark the Given.
2. Mark … Reflexive Sides / Vertical Angles
3. Choose a Method. (SSS , SAS, ASA)
4. List the Parts … in the order of the method.
5. Fill in the Reasons … why you marked the parts.
6. Is there more?
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Lesson 4-3: SSS, SAS, ASA 28
Problem 1 Given: AB CD BC DAProve: ABC CDA
Statements Reasons
Step 1: Mark the Given Step 2: Mark reflexive sidesStep 3: Choose a Method (SSS /SAS/ASA )Step 4: List the Parts in the order of the methodStep 5: Fill in the reasonsStep 6: Is there more?
A B
D C
SSS
Given
Given
Reflexive Property
SSS Postulate4. ABC CDA
1. AB CD2. BC DA3. AC CA
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Lesson 4-3: SSS, SAS, ASA 29
Problem 2 Step 1: Mark the Given Step 2: Mark vertical anglesStep 3: Choose a Method (SSS /SAS/ASA)Step 4: List the Parts in the order of the methodStep 5: Fill in the reasonsStep 6: Is there more?
SAS
Given
Given
Vertical Angles.
SAS Postulate
: ;
Pr :
Given AB CB EB DB
ove ABE CBD
E
C
D
AB
1. AB CB2. ABE CBD
3. EB DB4. ABE CBD
Statements Reasons
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Lesson 4-3: SSS, SAS, ASA 30
Problem 3
Statements Reasons
Step 1: Mark the Given Step 2: Mark reflexive sidesStep 3: Choose a Method (SSS /SAS/ASA)Step 4: List the Parts in the order of the methodStep 5: Fill in the reasonsStep 6: Is there more?
ASA
Given
Given
Reflexive Postulate
ASA Postulate
: ;
Pr :
Given XWY ZWY XYW ZYW
ove WXY WZY
Z
W Y
X 1. XWY ZWY
2. WY WY3. XYW ZYW
4. WXY WZY
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Lesson 4-4: AAS & HL Postulate 31
PostulatesAAS If two angles and a non included side of one triangle are
congruent to the corresponding two angles and side of a second triangle, then the two triangles are congruent.
HL If the hypotenuse and a leg of one right triangle are congruent to the hypotenuse and corresponding leg of another right triangle, then the triangles are congruent.
A
B C
D
E F
A
B C
D
E F
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Lesson 4-4: AAS & HL Postulate 32
Problem 1
Statements Reasons
Step 1: Mark the Given Step 2: Mark vertical anglesStep 3: Choose a Method (SSS /SAS/ASA/AAS/ HL )Step 4: List the Parts in the order of the methodStep 5: Fill in the reasonsStep 6: Is there more?
AAS
Given
Given
Vertical Angle Thm
AAS Postulate
Given: A C BE BDProve: ABE CBD
E
C
D
AB
1. A C2. ABE CBD
3. BE BD
4. ABE CBD
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Lesson 4-4: AAS & HL Postulate 33
Problem 2
3. AC AC2. AB AD
1. ,ABC ADCright s
Step 1: Mark the Given Step 2: Mark reflexive sidesStep 3: Choose a Method (SSS /SAS/ASA/AAS/ HL )Step 4: List the Parts in the order of the methodStep 5: Fill in the reasonsStep 6: Is there more?
HL
Given
Given
Reflexive Property
HL Postulate
Given: ABC, ADC right s AB ADProve: ABC ADC
CB D
A
4. ABC ADC
Statements Reasons