Think about it…

Angle Pair RelationshipsLearner Objective: As a result in learning, students should be able to classify triangles by side lengths and angles and determine the measurement of angles given measurement of another angle.

CCES: 7.G.2, 7.G.5, MP.4, MP.5, MP6

Think about it…• If a triangle has all equal sides and has a perimeter of

42cm, what is the length of each side? • If a triangle has 2 equal side lengths and has a

perimeter of 94 in, what are possible side lengths for the triangle?

• Draw a quadrilateral with one set of parallel sides and no right angles

• Can a triangle have more than one obtuse angle? Explain your reasoning

Angle Pair Relationships

How are special angle pairs identified?

Straight Angles

___________ are two rays that are part of a the same line and have only their endpoints in common.

Opposite rays

XY Z

XY and XZ are ____________.opposite rays

The figure formed by opposite rays is also referred to as a ____________. A straight angle measures 180 degrees.straight angle

Angles – sides and vertex

There is another case where two rays can have a common endpoint.

R

S

T

This figure is called an _____.angle

Some parts of angles have special names.

The common endpoint is called the ______,vertex

vertex

and the two rays that make up the sides ofthe angle are called the sides of the angle.

side

side

Naming Angles

R

S

T

vertex

side

side

There are several ways to name this angle.

1) Use the vertex and a point from each side.

SRT or TRSThe vertex letter is always in the middle.

2) Use the vertex only.

RIf there is only one angle at a vertex, then theangle can be named with that vertex.

3) Use a number.

1

1

Angles

Definitionof Angle

An angle is a figure formed by two noncollinear rays that have a common endpoint.

E

D

F

2

Symbols: DEF

2

E

FED

Angles

B

A

1

C

1) Name the angle in four ways.

ABC

1

BCBA

2) Identify the vertex and sides of this angle.

Point B

BA and BC

vertex:

sides:

Angles

W

Y

X1) Name all angles having W as their vertex.

1

2

Z

12

2) What are other names for ?1

XWY or YWX

3) Is there an angle that can be named ? W

No!

XWZ

Once the measure of an angle is known, the angle can be classified as one of three types of angles. These types are defined in relation to a right angle.

Types of Angles

A

right angle m A = 90

acute angle 0 < m A < 90

A

obtuse angle 90 < m A < 180

A

Angle Measure

Classify each angle as acute, obtuse, or right.

110°

90° 40°

50°

130° 75°

Obtuse

Obtuse

Acute

Acute Acute

Right

Angle Measure

Adjacent Angles

When you “split” an angle, you create two angles.

D

A

C

B 12

The two angles are called _____________adjacent angles

1 and 2 are examples of adjacent angles. They share a common ray.

Name the ray that 1 and 2 have in common. ____BD

adjacent = next to, joining.

Adjacent Angles

Definition ofAdjacentAngles

Adjacent angles are angles that:

M

J

N

R 12

1 and 2 are adjacentwith the same vertex R and

common side RM

A) share a common side

B) have the same vertex, and

C) have no interior points in common

Adjacent AnglesDetermine whether 1 and 2 are adjacent angles.

No. They have a common vertex B, but _____________no common side

1 2

B

12

G

Yes. They have the same vertex G and a common side with no interior points in common.

N

12J

LNo. They do not have a common vertex or ____________a common side

The side of 1 is ____LNJNThe side of 2 is ____

Definition ofComplement

aryAngles

30°

A

B C

60°D

E

F

Two angles are complementary if and only if (iff) The sum of their degree measure is 90.

mABC + mDEF = 30 + 60 = 90

Complementary and Supplementary Angles

30°

A

B C

60°D

E

F

If two angles are complementary, each angle is a complement of the other.

ABC is the complement of DEF and DEF is the complement of ABC.

Complementary angles DO NOT need to have a common side or even the same vertex.


15°H75° I

Some examples of complementary angles are shown below.

mH + mI = 90

mPHQ + mQHS = 9050°H

40° QP

S

30°60°T

U V

WZ

mTZU + mVZW = 90


Definition ofSupplement

aryAngles

If the sum of the measure of two angles is 180, they form a special pair of angles called supplementary angles.

Two angles are supplementary if and only if (iff) the sum of their degree measure is 180.

50°A B

C

130°

D

E F

mABC + mDEF = 50 + 130 = 180


105°H

75° I

Some examples of supplementary angles are shown below.

mH + mI = 180

mPHQ + mQHS = 18050°H

130°

Q

P S

mTZU + mUZV = 180

60°120°

T

U V

WZ

60° and

mTZU + mVZW = 180


Congruent Angles

Recall that congruent segments have the same ________.measure

_______________ also have the same measure.Congruent angles

Definition ofCongruent

Angles

Two angles are congruent iff, they have the same

______________.degree measure

50°B

50°

V

B V iff

mB = mV

Congruent Angles

1 2

To show that 1 is congruent to 2, we use ____.arcs

ZX

To show that there is a second set of congruent angles, X and Z, we use double arcs.

X Z

mX = mZ

This “arc” notation states that:

Congruent Angles

When two lines intersect, ____ angles are formed.four

12

34

There are two pair of nonadjacent angles.

These pairs are called _____________.vertical angles

Vertical Angles

Definition ofVerticalAngles

Two angles are vertical iff they are two nonadjacent angles formed by a pair of intersecting lines.

12

34

Vertical angles:

1 and 3

2 and 4

Vertical Angles

Theorem 3-1Vertical AngleTheorem

Vertical angles are congruent.

1

4

3

2m n

1 3

2 4

Vertical Angles

Find the value of x in the figure:

The angles are vertical angles.So, the value of x is 130°.130°

x°

Vertical Angles

Find the value of x in the figure:

The angles are vertical angles.(x – 10) = 125.(x – 10)°

125°x – 10 = 125.

x = 135.

Vertical Angles

Suppose A B and mA = 52.

Find the measure of an angle that is supplementary to B.

A52°

B52° 1

B + 1 = 1801 = 180 – B1 = 180 – 521 = 128°

Congruent Angles

1) If m1 = 2x + 3 and the m3 = 3x + 2, then find the m3

2) If mABD = 4x + 5 and the mDBC = 2x + 1, then find the mEBC

3) If m1 = 4x - 13 and the m3 = 2x + 19, then find the m4

4) If mEBG = 7x + 11 and the mEBH = 2x + 7, then find the m1

x = 17; 3 = 37°

x = 29; EBC = 121°

x = 16; 4 = 39°

x = 18; 1 = 43°

A B C

D

E

G

H

12

34

Congruent Angles

Documents

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