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From a point on the ground …

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From a point on the ground the angle of elevation of the bottom and top of a communication tower fixed on the top od a 20 m high building are 45° and 60° resptly .Find the hight of the tower
  • 1 answers

Sia ? 6 years, 6 months ago


Let AP = y m and BC = xm.
{tex}\therefore {/tex} In  {tex}\triangle B A P = \frac { B A } { P A } = \tan 45 ^ { \circ }{/tex} 
{tex}\Rightarrow \quad \frac { 20 } { y } = 1{/tex} 
{tex}\Rightarrow {/tex} y = 20 
In {tex}\triangle {/tex}CAP {tex}\frac { C A } { P A } = \tan 60 ^ { \circ }{/tex}
{tex}\Rightarrow \quad \frac { 20 + x } { y } = \sqrt { 3 }{/tex} 
{tex}\Rightarrow \quad 20 + x = y \sqrt { 3 }{/tex} (using y = 20) 
{tex}\Rightarrow \quad 20 + x = 20 \sqrt { 3 }{/tex} 
{tex}x = 20 \sqrt { 3 } - 20{/tex} 
{tex}= 20 ( \sqrt { 3 } - 1 ){/tex} 
{tex}= 20 \times ( 1 \cdot 73 - 1 ){/tex} 
Hence, height of the tower = 14.64 m

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