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The angle of elevation of the top of a vertical tower from a point A...

Mathematics
JAMB 1978

The angle of elevation of the top of a vertical tower from a point A on the ground is 60o. From a point B, 2 units of distance further away from the foot of the tower, the angle of elevation of the tower is 45o. Find the distance of A from the foot of the tower

  • A. 3 + \(\sqrt{3}\)
  • B. 5 + \(\sqrt{3}\)
  • C. 3 - \(\sqrt{3}\)
  • D. 1
  • E. \(\sqrt{3}\) + 1
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Correct Answer: Option E
Explanation

In < AFT: \(\frac{TF}{AF}\) = tan60º

therefore, TF = xtan60º ..................1

In < BFT: \(\frac{TF}{BF}\) = tan45º 

TF = ( 2  + x )tan45º .......................2

equating equations 1 and 2

xtan60º = ( 2 + x )tan45º

But tan60º = \(\sqrt3\) and tan45º = 1

x \(\sqrt3\) = 2 + x 

x \(\sqrt3\) - x = 2

x (  \(\sqrt3\) - 1) = 2

x = \(\frac{2}{(\sqrt3\)) - 1}\)

rationalizing the denominator x = \(\frac{2(\sqrt3 + 2)}{3 - 1}\) = \(\frac{2(\sqrt3 + 1)}{2}\) = \(\sqrt3\) + 1


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