Correct Marks 2
Incorrectly Marks -0.5
Q 1. At a point on a horizontal line through the base of a monument the angle of elevation of the top of the monument is found to be such that its tangent is {tex} \frac{1}{5} {/tex}. On walking 138 metres towards the monument the secant of the angle of elevation is found to be {tex} \frac{\sqrt{193}}{12} {/tex}. The height of the monument (in metre) is
42
49
35
56
{tex} \textbf{Shortcut approach} {/tex}
{tex} \textbf{Ist Case:} {/tex}
{tex} tan \theta =\frac{AB}{BC}=\frac{Perpendicular}{Base}=\frac{1}{5} {/tex}
{tex} \textbf{IInd Case:} {/tex}
{tex} Sec \alpha =\frac{AD}{BD}=\frac{Hypo}{Base} {/tex}
{tex} \frac{\sqrt{193}}{12} {/tex}
{tex} In\ \triangle ABD {/tex}
{tex} Hypo=\sqrt{193} {/tex}
{tex} Base=12 {/tex}
Then perpendicular = 7
(By pythagoras theorem)
In both case perpendicular will be equal
{tex} tan \theta =\frac{1 \times 7}{5 \times 7}=\frac{7\leftarrow Perpen}{35\leftarrow Base} {/tex}
{tex} AB = 42 m {/tex}