For-angles-a-b-c-R-with-a-b-c-pi-prove-the-following-identities-tan-1-a-2-tan-1-b-2-tan-1-c-2-tan-a-2-tan-b-2-tan-c-2-1-Help-

Question Number 115471 by manuel2456 last updated on 26/Sep/20

F o r a n g l e s a, b, c \in R w i t h a + b + c = π,

p r o v e t h e f o l l o w i n g i d e n t i t i e s :

\tan^{- 1} (\frac{a}{2}) + \tan^{- 1} (\frac{b}{2}) + \tan^{- 1} (\frac{c}{2}) = {(\tan (\frac{a}{2}) \tan (\frac{b}{2}) \tan (\frac{c}{2}))}^{- 1}

H e l p

Commented by Olaf last updated on 27/Sep/20

Sorry sir, are you sure your formula

is good ? Even for a particular value

it seems to be wrong .

For example try a = b = c = \frac{π}{3} .

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