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UPSC NDA I 2012 Mathematics Paper
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© examsnet.com
Question : 49
Total: 120
What is the value of
cos
{
cos
−
1
4
5
+
cos
−
1
12
13
}
?
63
∕
65
33
∕
65
22
∕
65
11
∕
65
Validate
Solution:
Put
cos
−
1
4
5
=
A
cos
A
=
4
5
⇒
s
i
n
A
=
3
5
cos
−
1
12
13
=
B
cos
B
=
12
13
⇒
Now,
cos
(
cos
−
1
4
5
+
cos
−
1
12
13
)
=
cos
(
A
+
B
)
=
cos
A
cos
B
−
s
i
n
A
A
s
i
n
B
=
(
4
5
)
(
12
13
)
−
(
3
5
)
(
5
13
)
=
48
65
−
15
65
=
33
65
.
© examsnet.com
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