Open Up Resources Logo

Lesson 1Relationships of Angles

Let’s examine some special angles.

Learning Targets:

  • I can find unknown angle measures by reasoning about adjacent angles with known measures.
  • I can recognize when an angle measures 90^\circ , 180^\circ , or 360^\circ .

1.1 Visualizing Angles

Use the applet to answer the questions.

  1. Which angle is bigger, a or b ?
  2. Identify an obtuse angle in the diagram.
open applet in presentation mode

1.2 Pattern Block Angles

  1. Look at the different pattern blocks inside the applet. Each block contains either 1 or 2 angles with different degree measures. Which blocks have only 1 unique angle? Which have 2?

  2. If you place three copies of the hexagon together so that one vertex from each hexagon touches the same point, as shown, they fit together without any gaps or overlaps. Use this to figure out the degree measure of the angle inside the hexagon pattern block.

    Three hexagons meet at one point creating an angle of 360 degrees
  3. Figure out the degree measure of all of the other angles inside the pattern blocks. (Hint: turn on the grid to help align the pieces.)
open applet in presentation mode

Are you ready for more?

We saw that it is possible to fit three copies of a regular hexagon snugly around a point.

Each interior angle of a regular pentagon measures 108^\circ . Is it possible to fit copies of a regular pentagon snugly around a point? If yes, how many copies does it take? If not, why not?

A pentagon is shown with an angle of 108 degrees

1.3 More Pattern Block Angles

  1. Use pattern blocks to determine the measure of each of these angles.

    Angles A, B, and C are shown
  2. If an angle has a measure of 180^\circ then the two legs form a straight line. An angle that forms a straight line is called a straight angle. Find as many different combinations of pattern blocks as you can that make a straight angle.

Use the applet if you choose. (Hint: turn on the grid to help align the pieces.)

open applet in presentation mode

1.4 Measuring Like This or That

Tyler and Priya were both measuring angle TUS .

Angle TUS is measured with a protractor. it is 40 degrees.
Priya thinks the angle measures 40 degrees. Tyler thinks the angle measures 140 degrees. Do you agree with either of them? Explain your reasoning.

Lesson 1 Summary

When two lines intersect and form four equal angles, we call each one a right angle. A right angle measures 90^\circ . You can think of a right angle as a quarter turn in one direction or the other.

two intersecting lines create 4 right angles

An angle in which the two sides form a straight line is called a straight angle. A straight angle measures 180^\circ . A straight angle can be made by putting right angles together. You can think of a straight angle as a half turn, so that you are facing in the opposite direction after you are done.

A straight angle is shown representing 180 degrees.

If you put two straight angles together, you get an angle that is 360^\circ . You can think of this angle as turning all the way around so that you are facing the same direction as when you started the turn.

An angle of 360 degrees is shown

When two angles share a side and a vertex, and they don't overlap, we call them adjacent angles.

Glossary Terms

adjacent angles

Adjacent angles share a side and a vertex.

In this diagram, angle ABC is adjacent to angle DBC .

Two angles are shown sharing a line segment. These angles are adjacent
right angle

A right angle is half of a straight angle. It measures 90 degrees.

A right angle is shown
straight angle

A straight angle is an angle that forms a straight line. It measures 180 degrees.

A straight angle is shown representing 180 degrees.

Lesson 1 Practice Problems

  1. Here are questions about two types of angles.

    Draw a right angle. How do you know it’s a right angle? What is its measure in degrees?

    Draw a straight angle. How do you know it’s a straight angle? What is its measure in degrees?

  2. An equilateral triangle’s angles each have a measure of 60 degrees.

    1. Can you put copies of an equilateral triangle together to form a straight angle? Explain or show your reasoning.

    2. Can you put copies of an equilateral triangle together to form a right angle? Explain or show your reasoning.

  3. Here is a square and some regular octagons.

    In this pattern, all of the angles inside the octagons have the same measure. The shape in the center is a square. Find the measure of one of the angles inside one of the octagons.

    a repeating pattern of octagons and squares

  4. The height of the water in a tank decreases by 3.5 cm each day. When the tank is full, the water is 10 m deep. The water tank needs to be refilled when the water height drops below 4 m.

    1. Write a question that could be answered by solving the equation 10-0.035d=4 .
    2. Is 100 a solution of 10-0.035d>4 ? Write a question that solving this problem could answer.

  5. Use the distributive property to write an expression that is equivalent to each given expression.

    1. \text-3(2x-4)
    2. 0.1(\text-90+50a)
    3. \text-7(\text-x-9)
    4. \frac45(10y+\text-x+\text-15)

  6. Lin’s puppy is gaining weight at a rate of 0.125 pounds per day.  Describe the weight gain in days per pound.