1. Grade 4 Unit 10 Geometry Measuring Angles

2. Angles
Cut Out

3. 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

4. Types of Angles
Acute angle: An angle whose measure is greater than zero degrees and less than 90 degrees
Which angles are not acute? 1 2 3 4 5

5. Types of Angles Right angle: Angle that measures 90 degrees
Which angle is a right angle? 1 2 3 4 5

6. Types of Angles
Obtuse angle: One angle measures greater than 90 degrees and less than 180 degrees
Which angle is an obtuse angle? 1 2 3 4 5

7. This is a ray. It only goes in one direction.
Straight Angle
Straight angle: A line that goes infinitely in both directions and measures 180 degrees
Which is not a straight angle? 2 1
This is a ray. It only goes in one direction.

8. 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

9. Which of the following measures closest to 450?
A B.
C D.

10. 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 D.
L L
This is about halfway This is too small.

11. What type of angle is formed between the hands of the clock shown below?
A. Right
B. Acute
C. Obtuse
D. Straight

12. What type of angle is formed between the hands of the clock shown below?
A. Right
B. Acute
C. Obtuse
D. Straight
Notice how the hands create a “cut out” angle on the clock.
Each minute is 6 degrees of 360 degrees total.
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

13. 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

14. 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

15. Identify an obtuse angle from the picture below.
A ACD
B DBC
C EBC
D. FBC

16. 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

17. In the diagram below, lines l and p intersect.
If the measure of is 1090, what is the measure of ?
1090
1000
710
190

18. In the diagram below, lines l and p intersect.
If the measure of is 1090, what is the measure of ?
1090
1000
710
190
Angle a and angle b combine to make a straight angle (1800). Subtract 1800 – 1090 to find angle b.