Bearings
Three-figure bearings - measuring and calculating bearings, back bearings, and bearings with trigonometry.
Learn
Bearings, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Measure and draw three-figure bearings
A bearing is measured FROM north, CLOCKWISE, and always written with three figures: due east is 090°, south-west is 225°. Draw the north line at the point you are measuring from first - everything hangs off it.
Calculate bearings using angle facts and parallel lines, including back bearings
North lines at different points are parallel, so alternate and co-interior angles carry bearings between them. The bearing back the way you came differs by 180°: if B is on a bearing of 070° from A, then A is on 250° from B - add 180, or subtract if that passes 360.
Solve bearings problems with scale drawings
Draw each leg in turn: north line, measure the bearing with a protractor, then the scaled distance along it. The answer - a distance and bearing home, say - is measured straight off the finished diagram, then converted back through the scale.
Combine bearings with Pythagoras' theorem and trigonometry
Perpendicular legs - say 8 km due east then 5 km due north - form a right-angled triangle: Pythagoras gives the direct distance and tan⁻¹ gives the angle, which you then convert into a bearing from north. On Higher, non-perpendicular legs bring in the sine and cosine rules.
Practice
Try a Bearings question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
The bearing of a tower T from a gate G is 110°. Using a north line at the tower, work out the bearing of G from T with the angle facts for parallel north lines.
- 070°
- 250°
- 290°
- 110°
Show the answer and the working
Answer: 290°
The north lines at G and T are parallel, and co-interior angles let you reach the back bearing 110° + 180°.
- The north lines at G and T are parallel.
- Reversing the direction adds 180° to a bearing below 180°.
- 110 + 180 = 290, so the bearing of G from T is 290°.