need help please really quick with trigonometry, find cos a and cot b exactly if a=15 and b=11

Answer 1

cos 15 = cos 30/2 = +- sqrt ( 1 + cos(30)/2) <--- half angle formula

= +- sqrt( 1 + sqrt(3)/2/ 2)

= +- sqrt( 1 + sqrt(3)/ 4)

= +- sqrt( 1 + sqrt(3)) / 2

cot(11) = 1 / tan(11) = 5.14455401597031013472322....