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If A+B+C=pi , prove that cos 2A +cos ...

If `A+B+C=pi `, prove that
`cos 2A +cos 2B +cos 2C=-1-4cos A cos Bcos C.`

A

`1+4 sin A cos B sin C`

B

`-1+4 sin A sin B cos C`

C

`-1-4 cos A cos B cos C`

D

`1+4 sin A sin B sin C`

Text Solution

Verified by Experts

The correct Answer is:
C
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