Grade 4
Unit 10
Geometry
Measuring Angles
Angles
Cut Out
Angles
 A shape formed by two rays sharing a common
endpoint; contains two rays and a vertex
vertex—point common to two
rays of a triangle or two sides
of a polygon
ray
vertex
ray—has one endpoint and
goes infinitely in one direction
ray
Types of Angles
 Acute angle: An angle whose measure is greater
than zero degrees and less than 90 degrees
Which angles are not acute?
4
1
3
2
5
Types of Angles
 Right angle: Angle that measures 90 degrees
Which angle is a right angle?
4
1
3
2
5
Types of Angles
 Obtuse angle: One angle measures greater than
90 degrees and less than 180 degrees
Which angle is an obtuse angle?
4
1
3
2
5
Straight Angle
 Straight angle: A line that goes infinitely in both
directions and measures 180 degrees
Which is not a straight angle?
1
2
This is a ray. It only
goes in one direction.
Measuring Angles
 You measure angles with a protractor.
Notice there are two scales. Be careful which 0 you start at.
900
This
point is 0
This
point is 0.
This point goes at the vertex of the angle
Which of the following measures closest to 450?
A.
B.
C.
D.
Which of the following measures closest to 450?
Compare each angle to 900 right angle (L)
A.
B.
L
L
These are too close to 900. This is greater than 900.
C.
L
This is about halfway.
D.
L
This is too small.
What type of angle is formed between the hands
of the clock shown below?
A. Right
B. Acute
C. Obtuse
D. Straight
What type of angle is formed between the hands
of the clock shown below?
Notice how the hands create a
“cut out” angle on the clock.
Each minute is 6 degrees of 360
degrees total.
A. Right
B. Acute
C. Obtuse
D. Straight
This clock shows a one fourth
fraction of the 360 degrees.
Watch your teacher work one
fourth of 360 degrees.
What degree do you think this
Right Angle will be?
Cut Out
The measure of the angle shown is —
A. between 00 and 450
B. between 450 and 900
C. between 900 and 1800
D. greater than 1800
The measure of the angle shown is —
A. between 00 and 450
B. between 450 and 900
C. between 900 and 1800 (obtuse angle)
D. greater than 1800
Identify an obtuse angle from the picture below.
A.
ACD
B.
DBC
C.
EBC
D.
FBC
Identify an obtuse angle from the picture below.
Obtuse angles are
greater than 900 (a right
angle) and less than a
straight angle (1800).
A.
ACD
B.
DBC
C.
EBC
D.
FBC
In the diagram below, lines l and p intersect.
If the measure of
is 1090, what is the measure
of
?
A.
B.
C.
D.
1090
1000
710
190
In the diagram below, lines l and p intersect.
If the measure of
is 1090, what is the measure
of
?
A.
B.
C.
D.
1090
1000
710
190
Angle a and angle b combine to make a straight
angle (1800). Subtract 1800 – 1090 to find angle b.