Question 1194430
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Two students ride on an helicopter to measure the
width of a lake. At a point 760 m above the lake, they are
able to measure using a lensatic sighting compass the angle of
depression on one side of the lake as 45° and the angle of
depression on the other side is 20°. What is the width of the lake?
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<pre>
If the two observation points at the lake shore are on the different (opposite) sides from the helicopter,
then the lake width is


     W = {{{760/tan(20^o)}}} + {{{760/tan(45^o)}}} = {{{760/0.364 + 760/1}}} = 2848 m  (rounded).    <ANSWER</U>



If the two observation points at the lake shore are on the same side from the helicopter,
then the lake width is


     W = {{{760/tan(20^o)}}} - {{{760/tan(45^o)}}} = {{{760/0.364 - 760/1}}} = 1328 m  (rounded).    <ANSWER</U>
</pre>

Solved.