Lesson 1.4: Angle Measure

Geometry CP

Mrs. Mongold

New Vocabulary

• Ray: is a part of a line, it has one endpoint and extends indefinitely in one direction.

** Always name rays with their endpoint first!!

• Opposite Rays: are two rays that share an endpoint AND form a straight line!

A B

X Y Z

Ray YX and ray YZ are opposite rays

Chapter 1 Foldable Flap 4

•Note when naming an angle with three letters, the vertex must always be the middle letter!

Example

• Name all the angles that have B as a vertex

AnswersAnswer:

Example

• Name a side of angle 5

Answer

• Ray BG• Ray BE• Ray BF

Chapter 1 Foldable Flap 4

Classify the angles

Congruent Angles

An angle bisector is a ray that divides an angle into two congruent angles

Example

• In the figure, Rays QP and QR are opposite rays, and ray QT bisects angle RQS.

S T

P

Q

R

Example

• If angle RQT = 6x + 5 and angle

SQT = 7x – 2 find RQT

S T

P

Q

R

Answer

• 6x + 5 = 7x – 2

7 = x

RQT = 6(7) + 5

= 42 + 5

= 47

Example

• Find angle TQS if angle RQS = 22a – 11 and angle RQT = 12a - 8

S T

P

Q

R

Answer

• 22a – 11 = 2(12a – 8) 22a – 11 = 24a – 16 5 = 2a a = 2.5

TQS = RQT = 12(2.5) – 8 = 30 – 8 = 22

How to use a protractor…

• First make sure the numbers are not backwards, then you line up the center of the circle on the bottom of the protractor with the vertex of the angle

This is the hole to be lined up with the vertex

Using a protractor…

• Use the small line through the circle to line up the side of the angle. DO NOT use the bottom of the protractor!!

Using a protractor…

• You always start at 0 on the side of the angle you lined up, this is how you tell to use the inside or outside numbers!

We are using the inside numbers here since 0 starts on the right!!

Answer

• The angle measure is approximately 730

Using a protractor continued…

• What is the measure of the ange?

Answer• 107o we are using the outside numbers

because the angles edge is to the left

Summarizing Lesson 1.4

• Write a note to the absent student explaining lesson 1.4, be very specific about the things we learned. You may use your foldable and notes if you would like. Write complete sentences!!!