A house has a bearing of $319^\circ$ from point A. Point B is 317 meters due east of A. The bearing of the house from point B is $288^\circ$. We need to find the distance between the house and point A.

GeometryTrigonometryBearingsLaw of SinesTriangles
2025/3/17

1. Problem Description

A house has a bearing of 319319^\circ from point A. Point B is 317 meters due east of A. The bearing of the house from point B is 288288^\circ. We need to find the distance between the house and point A.

2. Solution Steps

Let H be the location of the house.
Let A and B be the two points.
The bearing of H from A is 319319^\circ. This means the angle measured clockwise from North at A to the line AH is 319319^\circ. The angle between the North and AH measured counter-clockwise is 360319=41360^\circ - 319^\circ = 41^\circ.
The bearing of H from B is 288288^\circ. This means the angle measured clockwise from North at B to the line BH is 288288^\circ. The angle between the North and BH measured counter-clockwise is 360288=72360^\circ - 288^\circ = 72^\circ.
Since B is due east of A, the angle between the North line at A and the line AB is 9090^\circ.
In triangle ABH, let aa be the length of BH, bb be the length of AH, and cc be the length of AB, which is given as c=317c = 317 meters.
The angle HAB is the angle between the North at A and AB minus the angle between the North at A and AH. Thus, HAB=90(360319)=9041=49\angle HAB = 90^\circ - (360^\circ - 319^\circ) = 90^\circ - 41^\circ = 49^\circ.
The angle ABH is the angle between the North at B and BA minus the angle between the North at B and BH. The angle between the North at B and BA is 180180^\circ (since B is east of A). Therefore, ABH=180(360288)=18072=108\angle ABH = 180^\circ - (360^\circ - 288^\circ) = 180^\circ - 72^\circ = 108^\circ.
The sum of angles in a triangle is 180180^\circ, so AHB=180HABABH=18049108=23\angle AHB = 180^\circ - \angle HAB - \angle ABH = 180^\circ - 49^\circ - 108^\circ = 23^\circ.
Using the Law of Sines, we have:
asin(HAB)=bsin(ABH)=csin(AHB)\frac{a}{\sin(\angle HAB)} = \frac{b}{\sin(\angle ABH)} = \frac{c}{\sin(\angle AHB)}
We are looking for bb, the distance between A and H.
b=csin(ABH)sin(AHB)=317sin(108)sin(23)b = \frac{c \sin(\angle ABH)}{\sin(\angle AHB)} = \frac{317 \sin(108^\circ)}{\sin(23^\circ)}
b=317×0.95110.3907301.50.3907771.7b = \frac{317 \times 0.9511}{0.3907} \approx \frac{301.5}{0.3907} \approx 771.7

3. Final Answer

The distance between the house and point A is approximately 771.7 meters.

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