Question 864190
A pilot has just started on the glide path for a landing at an airport where the length of the runway is 9000'. The angles of depression from the plane to the ends of the runway are 17.5 degrees and 18.8 degrees. what is the altitude of the plane when it begins its descent? 
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Draw the picture::
You have 2 right triangles with base angles 18.8 and 17.5 at
each end of the runway.
Extend the runway line till it is directly below the plane;
let the extended base distance be "x":
Let the perpendicular height of the plane be "h":
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Equations:
(9000tan(18.8)tan(17.5))/(tan(18.8+tan(17.5)) = 1473.21 ft 
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Cheers,
Stan H.
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