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
Solution:
 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 60º 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.
Drawing Reflex Angles
To draw a reflex angle (i.e. angle greater than 180º and less than
360º), proceed as follows:
 Subtract the reflex angle from 360º. 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
Solution:
 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 120º and mark a small dot at the edge of
the protractor.
 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.
Activity 1

