Geometry

Lesson

As we have already seen in Naming Angles, there are two special angle types called supplementary and complementary. Apart from just being able to recognise them when we see them, we also need to know how to solve angle problems that use these special angle relationships.

Supplementary angles are two angles that sum to $180$180°. In the diagram, $\angle COD$∠`C``O``D` and $\angle DOE$∠`D``O``E` are supplementary angles. You might see supplementary angles as two angles that add up to a straight line.

Adjacent angles on a straight line are supplementary (sum to 180°)

Complementary angles are two angles that sum to $90$90°. In the diagram, $\angle DOC$∠`D``O``C` and $\angle COB$∠`C``O``B` are complementary. You might see complementary angles as two angles that add up to a right angle.

Adjacent angles forming a right angle are complementary (sum to 90°)

Let's have a look at these worked examples.

Calculate $x$`x` giving reasons for your answer.

Calculate $x$`x` giving reasons.

In the diagram, $AB$`A``B` is a straight line.

Solve for $x$

`x`. Give reasons.

Deduce the angle properties of intersecting and parallel lines and the angle properties of polygons and apply these properties