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#andy

\[\begin{array}{l}
B = \tan {5^o}.\tan {10^o}.\tan {15^o}.....\tan {80^o}.\tan {85^o}\\
B = \left( {\tan {5^o}.\tan {{85}^o}} \right)\left( {\tan {{10}^o}.\tan {{80}^o}} \right).....\left( {\tan {{45}^o}.\tan {{45}^o}} \right)\\
B = \left( {\tan {5^o}.\cot {5^o}} \right)\left( {\tan {{15}^o}.\cot {5^o}} \right).......\left( {\tan {{45}^o}.\cot {5^o}} \right)\\
B = 1.1.1......\,\,.1\\
B = 1
\end{array}\]