By using degree measurements to represent compass directions,
you can describe the heading, or direction, in which a plane is
traveling. in this system, 0° (360°) corresponds to due north,
90° corresponds to due east, 180° corresponds to due south,
and 270° corresponds to due west.
angles are measured in a clockwise direction. this is different
from measuring angles in standard position on a coordinate
system.
with this method you can describe a flight path in terms of
distances and headings. for example, suppose a plane flies 300 mi
on a heading of 45°; then the plane changes course and flies 200 mi
on a heading of 150°.
if you could determine the angle between the two “legs” of
the trip (b), you could then use the law of cosines to find
how far the plane has traveled from its point of departure (b).
because is parallel to , b is supplementary to bad, which
is 105°. thus b = 180° – 105° = 75°. using the law of cosines,
b2 = 3002 + 2002 – 2(300)(200) cos 75°, and b = 314.6 mi.

determine the heading on which the plane would have to travel to return to point a.

1. first use the law of sines to find bac, and then add 45°.

2. add 180°, to find the return heading.

suppose a plane flies 240 mi on a heading of 35°, then the plane changes course and flies 160 mi on a heading of 160°.
3. determine the heading on which the plane would have to travel to return to its point of origin.