Lesson 16 — Activity 1: Types of Angles
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Lesson 16 — Activity 1: Types of Angles
Getting Ready
In this first activity, you will review types of angles.
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Do you know that you can find many examples of angles in everyday life? The corner of a fridge is a right angle. There is an acute angle between your keyboard on the computer and the desk it sits on. When you lean back in your chair, the back
of the chair and your desktop are at an obtuse angle. When you open up a book and lay it flat, you get a straight angle.
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Try This:
Look at the picture below. There are many angles in houses. Can you spot some of them?
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You may see angles in the roof tops, the garage door, the columns of the porch, and in the windows. Can you find any other angles?
Types of Angles
An angle is the difference in direction between two lines.
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In the image above, the difference in direction between the two lines is 40°. A degree is a unit used to measure angles. A circle has 360 degrees in it and a right angle (shown below) has 90 degrees in it.
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You will also see right angles at intersections where streets and avenues meet, where walls meet floors, and on steps.
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Besides a right angle (90°), there are three other types of angles that you will look at in this lesson.
1.
Acute angles:
These are angles between 0 and 90 degrees.
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2. Obtuse angles: These are angles greater than 90 degrees but less than 180 degrees.
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3. Straight angles: These are angles that are 180 degrees, or a straight line.
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You will also see
straight angles
on roadways, hockey stick shafts, and ski poles!
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Try This:
Identify the type of angles shown below.
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The first angle, which measures 130 degrees, is an obtuse angle. The second angle, which measures 85 degrees, is an acute angle.
In addition to the angles above, there are two other angle descriptions to know about. These are complementary angles and supplementary angles.
Complementary angles are two angles that add up to 90°.
Supplementary angles are two angles that add up to 180°.
For example, if you were given an angle of 30 degrees and were asked to find the complementary angle to it, you would simply subtract 30° from 90°.
90° – 30° = 60°
If you had to find the supplementary angle to 30 degrees, you would subtract 30° from 180°.
180° – 30° = 150°
Self-check!