Question
A man standing in a point C of a ground. He observes a
flying an aero-plane in the east at an angle of elevation of 30° and after 30 seconds, he observes the same aero-plane in the west at an angle of elevation of 60°. If the aero-plane flies all along in a straight line at a height of 480√3 m, then its speed in km/h is:Solution
From the following figure, 
AB = ED = 480√3 AE = BD In Δ ABC, tan 30 = AB/BC 1/√3 = 480 √3/BC BC = 480 × 3 = 1440 In Δ EDC, tan 60 = ED/DC √3 = 480 √3/DC
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