Question

cot15/2=root2+root3+root4+root6

Answer 1

cot 2Ф =  (cot² Ф - 1 )/ 2 cot Ф  

let Ф = 15 deg          Cot 2 * 15 = cot 30 = √3

2√3 cot Ф = cot² Ф -1    =>    cot 15  = 2 + √3

Apply the above rule for cot 2Ф again with 2Ф = 15 deg