Question
$\sum\limits_{r = 1}^{89} {{{\log }_3}(\tan \,\,{r^o})} = $

Answer

d
(d) $\sum\limits_{r = 1}^{39} {{{\log }_3}(\tan {r^o}) = {{\log }_3}(\tan {{45}^o}} ) = {\log _3}1 = 0$.

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