Calculate Angles on Parallel Lines

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!