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JEE Advanced 2020 Concept Recapitulation Test 2 Paper 2
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© examsnet.com
Question : 51
Total: 54
If
cos
4
x
=
a
0
+
a
1
cos
2
x
+
a
2
cos
4
x
is true for all values of
x
∈
R
, then the value of
18
a
0
+
a
1
+
a
2
2
Your Answer:
Validate
Solution:
cos
4
x
=
2
cos
2
2
x
−
1
=
2
(
2
cos
2
x
−
1
)
2
−
1
=
2
(
4
cos
4
x
+
1
−
4
cos
2
x
)
−
1
=
8
cos
4
x
−
8
cos
2
x
+
1
∴
a
0
=
1
,
a
1
=
−
8
,
a
2
=
8
∴
5
a
0
+
a
1
+
a
2
=
5
© examsnet.com
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