Write 'True' or 'False' and justify your answer in each of the following:
If the height of a tower and the distance of the point of observation from its foot, both, are increased by $ 10 \% $, then the angle of elevation of its top remains unchanged.

AcademicMathematicsNCERTClass 10

Given:

If the height of a tower and the distance of the point of observation from its foot, both, are increased by \( 10 \% \), then the angle of elevation of its top remains unchanged.

To do:

We have to find whether the given statement is true or false.

Solution:



Let the height of the tower$=h$ and the distance of the point of observation from its foot$=x$

Let the angle of elevation$=\alpha$

$\therefore tan\alpha=\frac{h}{x}\ \ \ \ ...........\ ( i)$

Again, if the height of the tower and the distance of the point of observation from its foot are increased by $10\ %$,

Then the new height$=H=h+\frac{h\times 10}{100}=\frac{11h}{10}$

And, the new distance of the point of observation from its foot$=X=x+\frac{x\times 10}{100}=\frac{11x}{10}$

Let the new angle of elevation $=\beta$

Then $tan\beta=\frac{H}{X}$

$=\frac{\frac{11h}{10}}{\frac{11x}{10}}$ 

$=\frac{h}{x}$

$=tan\alpha\ \ \ \ .........\ ( from\ i)$

$\therefore \alpha=\beta$

Thus, prove that the angle of elevation of its top remains unchanged.

raja
Updated on 10-Oct-2022 13:28:58

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