# Lesson video

In progress...

Hi, I'm Miss Davies.

In this lesson, we're going to be looking at back bearings.

The bearing of B from A is 55 degrees.

We're going to work out the bearing of A from B.

Point B is 55 degrees in a clockwise direction from this north line.

To start off working out the bearing of A from B, going to extend the north line to get 180 degrees.

We now need to work out this angle.

Our north lines are parallel to one another.

This means that this angle is 55 degrees, as it is alternate to the original bearing that is given.

The bearing of A from B is 235 degrees, as 180 add 55 is 235.

Here are some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

The calculation for part a will be 180 add 70, which gives 220 degrees.

The calculation for part b is 180 add 115, giving the answer of 295 degrees.

The bearing of C from D is 305 degrees.

We're going to work out the bearing of D from C.

We can cut partition 305 degrees into 180 degrees and 125 degrees.

As our north lines are parallel, we can say that the bearing of D from C is 125 degrees, as these are alternate angles.

What do you notice about these pairs of bearings? The difference between a bearing and its back bearing is always 180 degrees.

The bearing of B from A is 255 degrees.

Eamon says, "The bearing A from B is 435 degrees because the difference between a bearing and its back bearing is always 180 degrees." Do you agree with Eamon? Eamon is not correct, as the bearing of A from B is 75 degrees.

Here is some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

If the bearing given is less than 180 degrees, you will add 180 degrees to give the back bearing.

If it is greater than 180 degrees, you just subtract 180 degrees to find the back bearing.

That's all for this lesson.

Thanks for watching.