dik cos 1/2 alpa = 12/13 dan alpa sudut lancip, tentukan tan x

cos ½a = 12/13
sin ½a = 5/13
tan ½a = 5/12

tan a = (2 tan ½a) / (1 - tan² ½a)
= (2.(5/12)) / (1 - (5/12)²)
= (5/6) / (1 - (25/144))
= (5/6) / (115/144)
= (5/6) × (144/115)
= 24/23