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 50o the alternate one would also be 50o
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 80o the corresponding one would also be 80o
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 180o
If the angle C was 80o , then the other co-interior angle D would be 180 - 80 = 100o
Have you made some notes?
Let's try some questions now finding missing angles using these rules!