View Full Version : Bearings and trigonometry?
trach171
Nov 14, 2009, 04:53 PM
Three towns A, B and C are connected by straight roads. B is due west of A, C is due south of B and the bearing of C from A is 220 degrees. If the distance from A to B is 300 km:
a) find the distance from A to C
b) find the bearing from A to C
jmjoseph
Nov 14, 2009, 05:15 PM
Based on what you have given, the distance between A and C is 466.7 km, and the bearing from A to C is 220 deg. The bearing from C to A is the reciprocal, 40 deg.
(Edited)
Unknown008
Nov 14, 2009, 09:31 PM
Sorry, but the distance is not good.
The easiest way to do it is by having a sketch in front of you.
26502
You can find angle BAC by having 270 - 220 = 50 degrees
Using cos, you know that
cos 50 = \frac {300}{AC}
Solving for AC will give you 466.7 m.
Then, the bearing is indeed 40 degrees
Unknown008
Nov 16, 2009, 01:27 AM
I used the diagonal of a 300km x 300km square, and I was obviously wrong. OOPS. I mis-read something. Thanks. Unk!
It's OK, it might have happened to anybody including myself :)