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If r and R are radii of the incircle and...

If r and R are radii of the incircle and circum-circle of `DeltaABC, ` then prove that :
`8rR{cos ^(2) A//2 +cos ^(2) B//2 +cos ^(2) C//2}`
`=2bc+2ca+2ab-a^(2) -b^(2) -c^(2).`

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