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Geometry and Spatial Sense

Geometry and Spatial Sense. Measuring and Constructing Angles with a Protractor. What is a Protractor???. A protractor is a tool that we use to measure and construct angles

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Geometry and Spatial Sense

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  1. Geometry and Spatial Sense Measuring and Constructing Angles with a Protractor

  2. What is a Protractor??? • A protractor is a tool that we use to measure and construct angles • It is shaped like a semi-circle and it has 2 rows of numbers along the round edge (the outer scale and the inner scale) • The centre of the zero line of the protractor is called the origin

  3. What does a Protractor Look Like? Zero Line Origin Outer Scale Inner Scale

  4. How is a Protractor Used? • There is a bit of a process involved to using a protractor, but once you’ve gotten the hang of it, it’s pretty simple • The hardest thing to remember is which scale to use (outer or inner)

  5. How is a Protractor Used to Measure Angles? • Step 1: Place the origin of the protractor on the vertex of the angle you are measuring • Step 2: Line up the bottom edge of the angle with the straight line at the bottom of the protractor • ***It should look like the picture in the next slide

  6. Picture of Step 1 and Step 2 Line up the bottom edge of the angle here Line up the vertex here

  7. How is a Protractor Used to Measure Angles? • Step 3: Take note of whether it is the inner scale or the outer scale of the protractor that says 0° where the zero line of the protractor lines up with the bottom edge of the angle – this will tell you which scale to follow to find your angle

  8. Picture of Step 3 We would use the inner scale here because we always start at 0° tomeasure an angle

  9. How is a Protractor Used to Measure Angles? • Step 4: Read where the top edge of the angle crosses the protractor over the scale you are using – either inner or outer (you can extend the line out with your pencil if it’s not long enough to cross the protractor scale) • This is your angle measurement

  10. Picture of Step 4 After extending the line past theedge of the protractor, we can easilysee that the top edge of the angle crosses at 48°

  11. Question • What kind of angle is the angle in our step-by-step instructions for measuring angles?

  12. Acute Angle

  13. How is a Protractor Used to Construct Angles? • Step 1: Draw a straight line or use a straight line that you have been given as your starting point, this becomes the bottom edge of your angle

  14. Picture of Step 1

  15. How is a Protractor Used to Construct Angles? • Step 2: Line up the zero line of your protractor with your straight line and make sure that one end of the line is at the origin

  16. Picture of Step 2

  17. How is a Protractor Used to Construct Angles? • Step 3: Take note of whether it is the inner scale or the outer scale of the protractor that says 0° where the zero line of the protractor lines up with the bottom edge of the angle – this will tell you which scale to follow to draw your angle

  18. Picture of Step 3 We would use the outer scale here because we always start at 0° to construct or draw an angle

  19. How is a Protractor Used to Construct Angles? • Step 4: Place a dot or an arrow at the angle measurement (on the correct scale) that you are asked to construct or draw – let’s use 110° this time

  20. Picture of Step 4

  21. How is a Protractor Used to Construct Angles? • Step 5: Line your ruler up between the dot or the point of the arrow and the end of your straight line that is lined up with the origin and draw another line

  22. Picture of Step 5

  23. Question • What kind of angle is the angle in our step-by-step instructions for measuring angles?

  24. Obtuse Angle

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