# 13. As observed from the top of a 75 m high lighthouse from the sea-level, the angles of depression of two ships are 30° and 45°. If one ship is exactly behind the other on the same side of the lighthouse, find the distance between the two ships.

Answers (1)
M manish

Given that,
Height of the lighthouse (AB) is 75 m from the sea level. And the angle of depression of two different ships are $\angle ADB = 30^0$ and $\angle ACB = 45^0$ respectively

Let the distance between both the ships be $x$ m.
According to question,

In triangle $\Delta ADB$,

$\tan 30^0 = \frac{AB}{BD}=\frac{75}{x+y} = \frac{1}{\sqrt{3}}$
$\therefore x+y = 75 \sqrt{3}$.............(i)

In triangle $\Delta ACB$,

$\tan 45^0 = 1 =\frac{75}{BC}=\frac{75}{y}$
$\therefore y =75\ m$.............(ii)

From equation (i) and (ii) we get;
$x = 75(\sqrt{3}-1)=75(0.732)$
$x = 54.9\simeq 55\ m$

Hence, the distance between the two ships is approx 55 m.

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