Solution:
e. Accurately subtracting two or more angles is an important step in computing the length of the
forward and back azimuths of a geodetic line based on the known geodetic positions of the ends of the
line. This process is known as inverse-position computation. Here are some precautions to observe.
(1) If the minuend is larger than the subtrahend, subtraction is performed. But keep in mind
when borrowing degrees or minutes that there are 60' in 1 and 60" in 1', and they must be carried over
in this manner.
Example: Subtract 254€ 15' 10" from 435€ 20' 59".
Solution:
435 20' 59"
-254 15' 10"
181€ 05' 49"
(2) If the minuend is smaller than the subtrahend, 360 must be added to the minuend. This
may be done without actually changing the value of the angle, as may be illustrated by an angle formed
by two radii of a circle.
Example: Subtract 94€ 59' 59" from 32€ 41' 30".
EN0591
4-6
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