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If circum-radius and in-radius of a tria...

If circum-radius and in-radius of a triangle ABC be 10 and 3 units respectively , then a cot A + cot B + cot C is equal to

A

13

B

26

C

39

D

none of these

Text Solution

Verified by Experts

We have,
a cot A + b cot B + c cot C
= 2R (cos A + cos B + cos C)
`=2R(1+4sinA/2sinB/2sinC/2)`
`=2R(1+r/R)=2(R+r)=2(10+3)=26`
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