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If cos alpha + cos beta =0 = sin ...

If ` cos alpha + cos beta =0 = sin alpha + sin beta , ` then `cos 2 alpha + cos 2 beta ` is equal to

A

`- 2 sin ( alpha + beta) `

B

`2 cos (alpha + beta)`

C

`2 sin ( alpha + beta)`

D

`-2 cos (alpha + beta)`

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The correct Answer is:
D
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