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For a regular of n sides, sides are a , and circum radius is R and in-radius =r, then r+R is

A

`a/2cot(pi/n)`

B

`acot(pi/(2n))`

C

`a/4cot(pi/(2n))`

D

`a/2cot(pi/(2n))`

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The correct Answer is:
D
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