In this activity, we will calculate missing angles in parallel lines.

There are rules we can learn to help us recognise certain angles, which will make it very easy for us!

*Make some notes and a quick sketch of each to help you - there are three rules!*

**1 Alternate angles**

These two angles are inside the parallel lines, on the opposite side of the line which crosses.

They form a Z shape.

The angles are the same, so if the top one was 50^{o }the** alternate **one would also be 50^{o}

**2 Corresponding**

These two angles hang below the parallel lines.

They form an F shape.

They can also be above the parallel lines in an upside down F shape.

The angles are the same, so if the top one was 80^{o }the** corresponding **one would also be 80^{o}

**3 Co-Interior**

These two angles are inside the parallel lines on the same side of the line crossing.

They form a C shape.

You will notice they are **not **the same, but they add up to 180^{o}

If the angle C was 80^{o} , then the other **co-interior **angle D would be 180 - 80 = 100^{o}

Have you made some notes?

Let's try some questions now finding missing angles using these rules!