Page 57 - Mathematics Coursebook

5.2 Drawing and measuring angles

5.2 Drawing and measuring angles

You need to use a protractor to draw and measure re"ex angles.
How to draw an angle of 245°
If you have a protractor that measures angles up to 360° you can measure 245° directly. If your
protractor only goes up to 180°, use one of these methods.

Method 1: 245° – 180° = 65°. Measure 180° Method 2: A whole turn is 360° and
(half a turn) and then another 65°. 360° – 245° = 115°.
Measure an obtuse angle of 115° and the re"ex
180° 180° + 65° = 245° angle between the two lines will be 245°.

65°

115°

245°

You can use a similar method to measure a re"ex angle. Either divide it into 180° + another angle, or
measure the smaller angle between the two line segments and subtract it from 360°.

) Exercise 5.2

1 Estimate the size of each of these angles. Then measure each one to see how close you were to the
correct answer.

c°

a° b°

d°
e°
g°

f °

h°

56 5 Angles