Vocabulary

1
(No Transcript)
2
Vocabulary
angle vertex acute angle right angle obtuse
angle straight angle
3
An angle is formed by two rays with a common
endpoint, called the vertex. An angle can be
named by its vertex or by its vertex and a point
from each ray. The middle point in the name
should always be the vertex. Angles are measured
in degrees. Use the symbol to show degrees.
4
Additional Example 1 Measuring an Angle with a
Protractor Use a protractor to measure the
angle.

• Place the center point of the protractor on the
  vertex of the angle.

5
Additional Example 1 Continued Use a protractor
to measure the angle.

• Place the protractor so that ray GH passes
  through the 0 mark.

6
Additional Example 1 Continued Use a protractor
to measure the angle.

• Using the scale that starts with 0 along ray
  GH, read the measure where ray GF crosses.

7
Reading Math
m?FGH is read the measure of angle FGH.
8
Additional Example 1 Continued Use a protractor
to measure the angle.

• The measure of ?FGH is 120. Write this as
  m?FGH 120.

9
Check It Out! Example 1 Use a protractor to
measure the angle.
G
I
H

• Place the center point of the protractor on the
  vertex of the angle.

10
Check It Out! Example 1 Continued Use a
protractor to measure the angle.
G
I
H

• Place the protractor so that ray HI passes
  through the 0 mark.

11
Check It Out! Example 1 Continued Use a
protractor to measure the angle.
G
I
H

• Using the scale that starts with 0 along ray
  HI, read the measure where ray HG crosses.

12
Check It Out! Example 1 Continued Use a
protractor to measure the angle.
G
I
H

• The measure of ?GHI is 70. Write this as m?GHI
  70.

13
Additional Example 2 Drawing an Angle with a
Protractor Use a protractor to draw an angle that
measures 80.

• Draw a ray on a sheet of paper.

14
Additional Example 2 Continued Use a protractor
to draw an angle that measures 80.

• Place the center point of the protractor on the
  endpoint of the ray.

• Place the protractor so that the ray passes
  through the 0 mark.

15
Additional Example 2 Continued Use a protractor
to draw an angle that measures 80.

• Make a mark at 80 above the scale on the
  protractor.

• Use a straightedge to draw a ray from the
  endpoint of the first ray through the mark you
  made at 80.

16
Check It Out! Example 2 Use a protractor to draw
an angle that measures 45.

• Draw a ray on a sheet of paper.

17
Check It Out! Example 2 Continued Use a
protractor to draw an angle that measures 45.

• Place the center point of the protractor on the
  endpoint of the ray.

• Place the protractor so that the ray passes
  through the 0 mark.

18
Check It Out! Example 2 Continued Use a
protractor to draw an angle that measures 45.

• Make a mark at 45 above the scale on the
  protractor.

• Use a straightedge to draw a ray from the
  endpoint of the first ray through the mark you
  made at 45.

19
An acute angle measures less than 90.
A right angle measures exactly 90.
20
An obtuse angle measures more than 90 and less
than 180.
A straight angle measures exactly 180.
21
Additional Example 3 Classifying Angles Classify
each angle as acute, right, obtuse, or
straight. A. B.
The angle measures less than 90, so it is an
acute angle.
The angle measures exactly 90, so it is a right
angle.
22
Check It Out! Example 3 Classify each angle as
acute, right, obtuse, or straight. A. B.
The angle measures less than 90, so it is an
acute angle.
The angle measures exactly 180, so it is a
straight angle.
23
Additional Example 4 Application A welder used
this piece of metal on his project. Classify ?X,
?Y, and ?Z.
?X right
The angle is marked as a right angle.
?Y obtuse
The angle measures more than 90 and less than
180.
?Z acute
The angle measures less than 90.
24
Check It Out! Example 4 A metal jeweler used this
piece of metal on her project. Classify ?A, ?B,
and ?D.
A
D
B
C
?A obtuse
The angle measures more than 90 and less than
180.
The angle measures less than 90.
?B acute
?D right
The angle is marked as a right angle.