A flag staff AB 4m high is placed on a vertical tower. The angle of elevation of foot of the flag staff B at two points D,E on the ground level and lying on either side of foot of the tower are α and 600 respectively with 4m and 23 m as the respective distances of these points from the foot of tower. The angle subtended by the flag staff at point D is
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a
tan−1219
b
tan−129
c
tan−1192
d
tan−1419
answer is D.
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Detailed Solution
From ΔBCE,cot60∘=23x⇒x=6 From △ACD,tan(θ+α)=104=52;tanα=32⇒tanθ+321−tanθ⋅32=52 ∵tan(A+B)=tanA+tanB1−tanAtanB⇒tanθ=419⇒θ=tan−1419Therefore, the correct answer is (4).
A flag staff AB 4m high is placed on a vertical tower. The angle of elevation of foot of the flag staff B at two points D,E on the ground level and lying on either side of foot of the tower are α and 600 respectively with 4m and 23 m as the respective distances of these points from the foot of tower. The angle subtended by the flag staff at point D is