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A tower is 100√3 metres high. Find the angle of elevation of its top from a point 100 metres away from its foot.

  • A.50º
  • B.40º
  • C.80º
  • D.60º

Answer: D

The tower is opposite the angle of elevation and the 100 m is the adjacent side, so the tangent gives the angle directly.

\[ \tan\theta = \frac{100\sqrt{3}}{100} = \sqrt{3} \]

\[ \theta = 60^{\circ} \]

The three standard tangents are worth knowing by sight: \( \tan 30^{\circ} = \tfrac{1}{\sqrt{3}} \), \( \tan 45^{\circ} = 1 \) and \( \tan 60^{\circ} = \sqrt{3} \). Since the tower is taller than the distance, the angle must exceed \( 45^{\circ} \).

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