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Year 7 Interactive Maths - Second Edition


Drawing Angles less than 180 with a Protractor

To draw an angle with a protractor, proceed as follows:
  • Draw a straight line (i.e. an arm of the angle).
  • Place a dot at one end of the arm.  This dot represents the vertex of the angle.
  • Place the centre of the protractor at the vertex dot and the baseline of the protractor along the arm of the angle.
  • Find the required angle on the scale and then mark a small dot at the edge of the protractor.
  • Join the small dot to the vertex with a ruler to form the second arm of the angle.
  • Label the angle with capital letters.


Example 1

Draw angle ABC = 60 degrees with a ruler and protractor

Solution:

Using a protractor to draw a 60 degree angle

  • Draw a straight line AB.
  • Place a dot at B.  This dot represents the vertex of the angle.
  • Place the centre of the protractor at B and the baseline of the protractor along the arm BA.
  • Find 60 on the scale and mark a small dot at the edge of the protractor.
  • Join the vertex B to the small dot with a ruler to form the second arm, BC, of the angle.
  • Mark the angle with a small arc as shown below.

Use a ruler to form the arm BC

 

Drawing Reflex Angles

To draw a reflex angle (i.e. angle greater than 180 and less than 360), proceed as follows:

  • Subtract the reflex angle from 360.  Then draw the resulting angle as described earlier.
  • The required angle is outside the one that has been drawn.
  • Mark the angle with a small arc.
  • Label the angle.


Example 2

Draw angle PQR = 240 degrees with a ruler and protractor

Solution:

To construct the reflex angle PQR, you need to draw an obtuse angle of size 120 degrees

  • Draw a straight line PQ.
  • Place a dot at Q.  This dot represents the vertex of the angle.
  • Turn the protractor upside down and place the centre of the protractor at Q and the baseline of the protractor along the arm PQ.
  • Use the outer scale to find 120 and mark a small dot at the edge of the protractor.

Using a protractor to draw a 240 degree angle

  • Then remove the protractor and join the vertex, Q, to the small dot with a ruler to form the second arm, QR, of the angle.
  • Mark the angle with a small arc as shown below.

Use a ruler to form the arm QR of the reflex angle PQR


Activity 1

Use a protractor to draw the following acute, obtuse and reflex angles.


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