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UPSC NDA 2 2012 Mathematics Paper
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© examsnet.com
Question : 40
Total: 120
From the top of a lighthouse
70
m
high with its base at sea level, the angle of depression of a boat is
15
∘
. The distance of the boat from the foot of the lighthouse is :
70
(
2
−
√
3
)
m
70
(
2
+
√
3
)
m
70
(
3
−
√
3
)
m
70
(
3
+
√
3
)
m
Validate
Solution:
AB
is a lighthouse.
Let
AC
=
x
m
.
tan
15
∘
=
70
x
√
3
−
1
√
3
+
1
=
70
x
x
=
70
(
√
3
+
1
)
√
3
−
1
C
=
70
(
√
3
+
1
)
√
3
−
1
×
√
3
+
1
√
3
+
1
=
70
×
2
(
2
+
√
3
)
2
⇒
x
=
70
(
2
+
√
3
)
m
.
© examsnet.com
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