pi / 12 = 15 °
pi / 12 = 30 ° / 2
sin 30 ° = 1 / 2
cos 30 ° = sqrt ( 3 ) / 2
cot ( theta / 2 ) = ( 1 + cos theta ) / sin theta
cot 15 ° = ( 1 + cos 30 ° ) / sin 30 °
cot 15 ° = [ 1 + sqrt ( 3 ) / 2 ] / ( 1 / 2 )
cot 15 ° = 2 * [ 1 + sqrt ( 3 ) / 2 ]
cot 15 ° = 2 * [ 2 / 2 + sqrt ( 3 ) / 2 ) ]
cot 15 ° = 2 * [ 2 + sqrt ( 3 ) ] / 2
cot 15 ° = 2 + sqrt ( 3 )
cot pi / 12 = cot 15 ° = 2 + sqrt ( 3 )
cot (pi/12)
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