# Geometry Lesson Plan Section 4.1 Triangles and Angles

Electronics - Devices

Oct 10, 2013 (5 years and 3 months ago)

115 views

Geometry
Lesson Plan

Section
4
.1
Triangles and Angles

1.

Objectives
: SWBAT

o

Identify attributes of triangles
.

o

Classify
tri
angles
by sides and angles

o

Apply the Triangle Sum and Exterior Angle theorems

2.

Vocabulary
:

Set 1:

vertices
, interior angle, exterior angle, vertices

Set
2
:

equilateral ▲,

scalene

▲,

isosceles ▲, base, base angles

Set
3
:

acute ▲, obtuse ▲,

right ▲, equiangular ▲
, hypotenuse,

leg

3
.
Theorems
:

4.1

Triangle Sum Theorem.
The sum of the interior angles in a triangle is 180
°
.

4.2 E
xterior Angle Theorem
.

The measure of an exterior is equal t
o

the sum of the two

remote

interior angles.

4
.
Instruction

a) Vocabulary
S
et

A

A

ABC

Vertices
: A, B, and C

Sid
es:
AB, BC, and CA

B

C

have a common vertex.

Opposite side
:

Across from the vertex: AB is opposite to C.

Interior angles:

3,

5, and

6

Exterior angles:

1,

2,

4, and

7

R

1 2

3

4 5 6
S

T

7

Note:

When we say

A, it means the interior angle at A
;

3

b) Vocabulary
Sets B and C

Classify by Sides

Equilateral Triangle

Isosceles Triangle

Scalene triangle

3 congruent sides

2 congruent sides

No congruent sides

Classify by Angles

Acute Triangle

Equia
ngular

Triangle

Right Triangle

Obtuse Triangl
e

3 acute angles

3 congruent angles

1 right angle

1 obtuse angle

c) Special Sides and Angles

Right Triangles

Isosceles Triangle

hypotenuse

leg

leg

base

leg

leg

Example
:

X

2

Classify
▲XYZ. _________ __________

Name the
base
(s). ______

1 3 4 5

Name the
leg
(s). _______

Name the
interior angles
. ________

Y

Z

Name the
exterior angles
. ________

e Measurement

Triangle Sum Theorem.

The sum of the interior angles in a triangle is 180
°
.

For all triangles

1.

2.

A

B

45° x

30°

32°

75° x

C

m

A +
m

B +
m

C = 180°

Exterior Angle Theorem
.

The measure of an exterior is equal to the sum of the two remote interior angles.

For all triangles

1

2 3 4

m

1 =
m

3 +
m

5

5

m

4 =
m

2 +
m

5

6

m

6 =
m

2 +
m

3

Examples

52°

98° 30° 153° x°

111°

55°

x° y°

67°

50° 82°

75° x° y° z°

5
.

Assessment:

Questioning and Discussion of homework problems the following day.

6
.
Homework:

Pg. 198; 1

30

Geometry Lesson Plan

Section 4.1
Triangles and Angles

(Day 2)

1.

Objective
:
Solve problem
s using the Triangle Sum and Exterior Angle theorems

Triangle Sum Theorem.

Exterior Angle Theorem
.

The sum of the interior angles is 180
°
.

The measure of an exterior is equal to the

sum of the two remote interior angles.

A

R

B

C U S T

m

A +

m

B +
m

C = 180°

m

USR =

m

R +
m

T

2. Examples:

Solve for “x”

1.

2.

9x + 10 10x

4

15x + 2

7x

11 5x + 12

7x + 124

3.
Given

▲ABC.

4.

Write an
equation of a line with a

slope of ½ and through (6,
-
5).

a) Solve for “x”

b) Find the measurement of each angle

c) Classify the triangle

m

A = x°

m

C = 2x°

m

C = (2x + 7)°

5.

Assessmen
t:

Questioning and Discussion of homework problems the following day.

6.
Homework:

Pg. 199; 31

39, 47, 61

65

Study Guide: Section 4.1
Triangles and Angles

Notation: ▲ABC

A

Vertices
: A, B, and C

Sides:
AB, BC, and CA

B

C

have a common vertex.

Opposite sides
:

Across from the vertex:

AB is opposite to

C.

Interior angles: ________
____________ Exterior angles:_____________________________

Classify by Sides

___________________

___________________

________________________

3 congruent sides

2 congruent sides

No congruent sides

Classify by Angles

_____________

___
______________

______________

________________

3 acute angles

3 congruent angles

1 right angle

1 obtuse angle

1.

X

2

Classify
▲XYZ. _________ __________

Name the
base
(s). ______

1

3 4 5

Name the
leg
(s). _______

Name the
interior angles
. ________

Y

Z

Name the
exterior angles
. ________

Triangle Sum Theorem.

Exterior Angle Theorem
.

The sum of the interior angles is 180
°
.

The mea
sure of an exterior is equal to the

sum of the two remote interior angles.

A

R

B C U

S T V

m

A +

m

B +
m

C = 180°

m

USR =

m

R +
m

T

Warm up 10/16/07

Find “x” and “y”

1.

y

42°

x

51°