Question

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Answer 1

$tgfrac{a}{2}=frac{1-cosa}{sina}\\tgfrac{pi}{12}= frac{1-cosfrac{pi}{6}}{sinfrac{pi}{6}} = frac{1-frac{sqrt3}{2}}{frac{1}{2}} = frac{2-sqrt3}{2cdot frac{1}{2}} =2-sqrt3$