Q.From a point on the roof of a five-storey building, the angle of elevation to the top of a monument is 60°, and the angle of depression to its base is 30°. If the height of the building is 16 meters, find the height of the monument and the distance from the building to the monument.

Let AB be a five-storey building, from the rooftop point A of which the angle of elevation to the top of a monument (point C) is 60°, and the angle of depression to its base (point D) is 30°. The height of the building is AB = 16 meters. ∴ ∠CAE = 60° [Assume AE || BD] ∠EAD = 30° ∴ ∠ADB = ∠EAD = 30° From right-angled triangle ABD: \(\tan 30^\circ = \frac{AB}{BD} = \frac{16}{BD}\) ⇒ \(\frac{1}{\sqrt{3}} = \frac{16}{BD}\) ⇒ \(BD = 16\sqrt{3}\) ∴ AE = BD = \(16\sqrt{3}\) From right-angled triangle AEC: \(\tan 60^\circ = \frac{CE}{AE} = \frac{CE}{16\sqrt{3}}\) ⇒ \(\sqrt{3} = \frac{CE}{16\sqrt{3}}\) ⇒ \(CE = 16\sqrt{3} \times 3 = 48\) ∴ CD = CE + ED = CE + AB = 48 + 16 = 64 ∴ The height of the monument is 64 meters and the distance from the building to the monument is \(16\sqrt{3}\) meters.
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