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Byju's Answer
Standard XII
Physics
Multiplication with Vectors
Find the valu...
Question
Find the value of
cos
π
5
+
cos
2
π
5
+
cos
6
π
5
+
cos
7
π
5
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Solution
cos
π
5
+
cos
2
π
5
+
cos
6
π
5
+
cos
7
π
5
rearranging
=
cos
π
5
+
cos
6
π
5
+
cos
2
π
5
+
cos
7
π
5
=
cos
π
5
+
cos
(
π
+
π
5
)
+
cos
2
π
5
+
cos
(
π
+
2
π
5
)
as cos
(
π
+
θ
)
=
-cos
θ
=
cos
π
5
−
cos
(
π
5
)
+
cos
2
π
5
−
cos
(
2
π
5
)
=
0
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0
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