A) 30 m
B) 60 m
C) 50 m
D) None of these
Correct Answer: C
Solution :
\[\tan \alpha =\tan (\varphi -\theta )\] \[\tan \alpha =\frac{1}{6}=\frac{\frac{20+h}{70}-\frac{h}{70}}{1+\frac{(20+h)\,h}{{{(70)}^{2}}}}\] \[\Rightarrow \] \[{{(70)}^{2}}+20h+{{h}^{2}}=(6)(70)(20)\] \[\Rightarrow \] \[{{h}^{2}}+20h+70(70-120)=0\] \[\Rightarrow \] \[{{h}^{2}}+20h-(50)\,(70)=0\] \[\Rightarrow \] \[h=\frac{-20\pm \sqrt{400+(4)(50)(70)}}{2}=50m\].You need to login to perform this action.
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