Draw and label the situation before selecting a rule. Bearings are measured clockwise from north and written with three digits. Draw parallel north lines at both locations. A reverse bearing differs by 180, reduced to [0,360). For example, the reverse of 065 is 245. An elevation angle is measured up from a horizontal line; a depression angle is measured down. Parallel horizontals give equal alternate angles. In the sketch, tanalpha= hd. Add the observer’s eye height when finding a total building height. In a non-right triangle, use the sine or cosine rule after deriving the interior angles from the bearings.

Draw and label the situation before selecting a rule. Bearings are measured clockwise from north and written with three digits. Draw parallel north lines at both locations.

A reverse bearing differs by \(180^\circ\), reduced to \([0^\circ,360^\circ)\). For example, the reverse of \(065^\circ\) is \(245^\circ\).

An elevation angle is measured up from a horizontal line; a depression angle is measured down. Parallel horizontals give equal alternate angles. In the sketch, \(\tan\alpha=\dfrac{h}{d}\).

Add the observer’s eye height when finding a total building height. In a non-right triangle, use the sine or cosine rule after deriving the interior angles from the bearings.

Trigonometry

International Baccalaureate Mathematics: Analysis and Approaches Higher Level

Bearings, Elevation and Depression

Bearings, Elevation and Depression