Unit 7, Lesson 15
Reasoning about Angles (Part 2)
Grade 4
Warm-up
How many angles do you see in the folded paper heart?
Activity 1
Find the measurement of each shaded angle. Show how you know.
4 angles. A. Right angle partitioned into two angles. One shaded green, one labeled 62 degrees. B. Straight angle partitioned into 3 angles. One labeled 71 degrees, one shaded yellow, one marked with a right angle symbol. C. Horizontal straight line partitioned into 2 angles on top by a ray and 2 angles below by another ray. On top, left angle shaded blue, right angle labeled 1 hundred 8 degrees. On the bottom, left angle labeled 1 hundred 54 degrees, right angle shaded red. D. Two straight lines intersect and partitioned into 2 angles on top and 2 angles below. On top, smaller angle on the left shaded green and bigger angle on the right unlabeled. On the bottom, bigger angle on the left shaded yellow, smaller angle on the right, labeled 43 degrees.
Activity 2
Your teacher will give you either a problem card or a data card. Do not show or read your card to your partner.
Pause here so your teacher can review your work. Ask your teacher for a new set of cards and repeat the activity. Switch roles with your partner.
Student Section Summary
We learned ways to name angles based on their measurements.
-
Acute angles are angles that measure less than .
-
Right angles are angles that measure .
-
Obtuse angles are angles that measure greater than .
-
Straight angles are angles that measure .
We also solved problems about angles.
Examples:
If two angles make a right angle or a straight angle, we can use the size of one angle to find the other.
The shaded angle here must be because it makes a right angle when combined with the angle.
We know that the full turn of a clock measures , so we determined that the long hand makes:
- A angle every hour.
- A angle every one-half hour.
- A angle every 15 minutes.
- A angle every 10 minutes.