Calculate Missing Angles

In this activity, you will need to find missing angles.

Missing angles on a straight line:

Angles on a straight line add up to 180°

To calculate a missing angle on a straight line, take away the known angle from 180°

180° - 55° = 125°

Missing angles in a full turn:

Angles in a full turn add up to 360°

To calculate a missing angle in a full turn, take away the known angle from 360°

360° - 105° = 255°

Missing angles on intersecting lines:

All four angles will add up to 360°

Opposite angles on a cross are equal.

360° - 72° - 72° = 216°

216° ÷ 2 = 108°

Both missing angles are 108°

Missing angles in quadrilaterals:

A quadrilateral is any shape with four sides.

For example: square, rhombus, trapezium, parallelogram.

The angles in a quadrilateral add up to to 360°

360° - 82° - 82° - 98° = 98°

We can also see that, in this trapezium, the two top angles are the same, as are the two bottom angles.

Let's get started on some questions now.