Lesson 1.4: Angle Measure

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Lesson 1.4 Angle Measure

• Geometry CP
• Mrs. Mongold

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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
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Chapter 1 Foldable Flap 4

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

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Example

• Name all the angles that have B as a vertex

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Answers
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Example

• Name a side of angle 5

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Answer

• Ray BG
• Ray BE
• Ray BF

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Chapter 1 Foldable Flap 4
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Classify the angles
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Congruent Angles
An angle bisector is a ray that divides an angle
into two congruent angles
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Example

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

S
T
R
Q
P
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Example

• If angle RQT 6x 5 and angle
• SQT 7x 2 find RQT

S
T
R
Q
P
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Answer

• 6x 5 7x 2
• 7 x
• RQT 6(7) 5
• 42 5
• 47

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Example

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

S
T
R
Q
P
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Answer

• 22a 11 2(12a 8)
• 22a 11 24a 16
• 5 2a
• a 2.5
• TQS RQT
• 12(2.5) 8
• 30 8
• 22

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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
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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!!

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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!!
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Answer

• The angle measure is approximately 730

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Using a protractor continued

• What is the measure of the ange?

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Answer

• 107o we are using the outside numbers because the
  angles edge is to the left

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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!!!