Page 60 - Mathematics Coursebook

5.3 Calculating angles

3 The angles in each of these diagrams are all the same size. How big is each one?

a b

4 Calculate the size of angle ABC in each of these triangles.
a B b c
A C C
28° 38°

A 25°
57° 49° B
A C B
5 Calculate the size of angle BCD in each of these diagrams.
a B BB b AA C C C D c A AA
A
D D
B BB
125°
125°
125°
132°
55° 132°132°
55°55°
30°
30°30° C CC
60° 60°
60°
AA C CC D DD 71°71°
A
71°
B BB
D DD
6 Three angles of a quadrilateral are 60°, 80° and 110°. How big is the fourth angle?
7 Calculate the sizes of the lettered angles in these quadrilaterals.
100°
63° 172°
40°
95° 35°
b°
35° c°
110° a° 62°

8 If all the angles of a quadrilateral are equal, what can you say about the quadrilateral?

9 Maha measures three of the angles of a quadrilateral.

The angles are 125°, 160° and 90°.

How do you know she has made a mistake?
How do you know she has made a mistake?
10 One angle of a quadrilateral is 150°. The other three angles are all the same size as each other.
How big are they?

5 Angles 59