The bearing of B from A is 310°, find the bearing of A from B

Step by step

The question

Question: the bearing of B from A is 310°: find the bearing of A from B.

1 Draw the north line

A bearing starts at the north line.

It is measured clockwise, the way a clock turns, and written with 3 figures.

At B we draw a north line too.

The two north lines are parallel.

2 Turn round

From B back to A is the opposite direction: half a turn more, 180°.

310 is more than 180, so we take 180 away: 130°.

Adding would go past 360°.

Why 180?

The north lines are parallel.

The angles between the path and the two north lines add up to 180°, as in the parallel lines lesson.

Careful!

A bearing is under 360°.

Over 180°, we take 180 away.

3 Check

Let's check: the two bearings differ by exactly 180°, half a turn.

So it is right!

Let's look back.

First: draw the north line.

Then: turn round.

Last: check.