cos²(5⁰)+cos²(10⁰)+...+cos²(360⁰)
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Answer:
Answer
Correct option is
A
4
3
cos
2
10
o
−cos10
o
.cos50
o
+cos
2
50
o
=cos
2
50
o
−sin
2
10
o
+1−(2.cos50
o
.cos10
o
).
2
1
=cos60
o
.cos40
o
+1−
2
1
(cos(60
o
)+cos(40
o
))
(∵cos
2
A−sin
2
B=cos(A+B).cos(A−B) and 2cosA.cosB=cos(A+B)+cos(A−B))
=
2
1
cos40
o
+1−
2
1
(
2
1
+cos40
o
)
=1−
4
1
=
4
3
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