Year 10 Interactive Maths - Second Edition

Composite Figures

For trigonometric problems involving a composite figure, first decide whether to use sine, cosine or tangent, and then calculate the required length or angle.

Example 17

In the given diagram, find:
a.  x
b.  y

Solution:

Using a Construction Line

To solve some trigonometric problems, we need to convert the given triangle into two right-angled triangles by drawing a perpendicular construction line from the vertex to the opposite side.

Example 18

Find BC in the given diagram, rounded to 2 decimal places.

Solution:

Draw BD perpendicular to AC.  Let BD = x cm, BC = y cm.