A pole \[5m\] high is fixed on the top of the tower. The angle of elevation of the top of the poles as observed from a point \[A\] on the ground is \[60\] degree and the angle of depression of the point\[A\] from the top of the tower is \[45\]degree. Find the height of the tower.
Answer
605.4k+ views
Hint: Draw the figure of the tower then using a vertically opposite angle concept, try to equal the angles.Using the trigonometric ratio concept , find the height of the tower by taking two different triangles and solve for the height.
Formula used:
Tangent trigonometric ratio concept.
\[\tan {{60}^{\circ }}=\sqrt{3}\]
Complete step by step answer:
irst, by the help of the above information, we draw the figure of the question.
Let \[BC\] be the height of the tower and \[CD\] be the pole of height \[5m\] fixed on the top of the tower.
Take
\[BC=hm\].
Also,
The angle of elevation of top of the pole from the point \[A\] on the ground be \[60\] degree and the angle of depression of the point \[A\] from the top of the tower be \[45\] degree, that is \[\angle BAD={{60}^{\circ }}\] and \[\begin{align}
& \angle BAC={{45}^{\circ }} \\
& \\
\end{align}\]
In right angled triangle\[ABC\], we have;
\[\begin{align}
& \tan {{45}^{\circ }}=\dfrac{BC}{AB} \\
& \Rightarrow 1=\dfrac{h}{AB} \\
& \Rightarrow AB=h \\
\end{align}\]
Also in the right angled triangle\[ABD\], we have;
\[\begin{align}
& \tan {{60}^{\circ }}=\dfrac{BD}{AB} \\
& \Rightarrow \sqrt{3}=\dfrac{BC+CD}{AB} \\
& \Rightarrow \sqrt{3}=\dfrac{h+5}{AB} \\
& \Rightarrow AB=\dfrac{h+5}{\sqrt{3}} \\
\end{align}\]
Comparing both the equation, we get;
\[\begin{align}
& \Rightarrow \sqrt{3}h-h=5 \\
& \Rightarrow h(\sqrt{3}-1)=5 \\
\end{align}\]
Now on rationalizing, we obtain;
\[\Rightarrow h=\dfrac{5}{\sqrt{3}-1}\times \dfrac{\sqrt{3}+1}{\sqrt{3}+1}\]
\[\Rightarrow h=\dfrac{5(\sqrt{3}+1)}{(\sqrt{3{{)}^{2}}}-{{1}^{2}}}=\dfrac{5(\sqrt{3}+1)}{2}\]
\[AB\] is equal to \[\dfrac{h+5}{\sqrt{3}}\] and \[h\] has above equation, so solving these we get;
\[\begin{align}
& \Rightarrow h=\dfrac{5(\sqrt{3}+1)}{2} \\
& \Rightarrow h=\dfrac{5\times (1.732+1)}{2} \\
& \Rightarrow h=\dfrac{5\times (2.732)}{2} \\
& \Rightarrow h=\dfrac{13.66}{2} \\
& \Rightarrow h=6.83m \\
& \\
\end{align}\]
Putting the value of \[\sqrt{3}\] that is equal to \[1.732\] and solving for \[h\] we get;
\[\begin{align}
& h=6.83m \\
& \\
\end{align}\]
That is the height of the tower is \[6.83m\].
Note: We have to only find the height of the tower so do not consider the triangle for the poles.
Use an alternative angle concept to make the lower angles equal.
Formula used:
Tangent trigonometric ratio concept.
\[\tan {{60}^{\circ }}=\sqrt{3}\]
Complete step by step answer:
irst, by the help of the above information, we draw the figure of the question.
Let \[BC\] be the height of the tower and \[CD\] be the pole of height \[5m\] fixed on the top of the tower.
Take
\[BC=hm\].
Also,
The angle of elevation of top of the pole from the point \[A\] on the ground be \[60\] degree and the angle of depression of the point \[A\] from the top of the tower be \[45\] degree, that is \[\angle BAD={{60}^{\circ }}\] and \[\begin{align}
& \angle BAC={{45}^{\circ }} \\
& \\
\end{align}\]
In right angled triangle\[ABC\], we have;
\[\begin{align}
& \tan {{45}^{\circ }}=\dfrac{BC}{AB} \\
& \Rightarrow 1=\dfrac{h}{AB} \\
& \Rightarrow AB=h \\
\end{align}\]
Also in the right angled triangle\[ABD\], we have;
\[\begin{align}
& \tan {{60}^{\circ }}=\dfrac{BD}{AB} \\
& \Rightarrow \sqrt{3}=\dfrac{BC+CD}{AB} \\
& \Rightarrow \sqrt{3}=\dfrac{h+5}{AB} \\
& \Rightarrow AB=\dfrac{h+5}{\sqrt{3}} \\
\end{align}\]
Comparing both the equation, we get;
\[\begin{align}
& \Rightarrow \sqrt{3}h-h=5 \\
& \Rightarrow h(\sqrt{3}-1)=5 \\
\end{align}\]
Now on rationalizing, we obtain;
\[\Rightarrow h=\dfrac{5}{\sqrt{3}-1}\times \dfrac{\sqrt{3}+1}{\sqrt{3}+1}\]
\[\Rightarrow h=\dfrac{5(\sqrt{3}+1)}{(\sqrt{3{{)}^{2}}}-{{1}^{2}}}=\dfrac{5(\sqrt{3}+1)}{2}\]
\[AB\] is equal to \[\dfrac{h+5}{\sqrt{3}}\] and \[h\] has above equation, so solving these we get;
\[\begin{align}
& \Rightarrow h=\dfrac{5(\sqrt{3}+1)}{2} \\
& \Rightarrow h=\dfrac{5\times (1.732+1)}{2} \\
& \Rightarrow h=\dfrac{5\times (2.732)}{2} \\
& \Rightarrow h=\dfrac{13.66}{2} \\
& \Rightarrow h=6.83m \\
& \\
\end{align}\]
Putting the value of \[\sqrt{3}\] that is equal to \[1.732\] and solving for \[h\] we get;
\[\begin{align}
& h=6.83m \\
& \\
\end{align}\]
That is the height of the tower is \[6.83m\].
Note: We have to only find the height of the tower so do not consider the triangle for the poles.
Use an alternative angle concept to make the lower angles equal.
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