if cos thita =12upon13 , 0
cos theta =12/13
cos^2 theta= (12/13)^2
sin^2 theta = 1-(12/13)^2
= (169-144)/169
= 25/169
sin theta = 5/13
(sin ^2 theta - cos ^2 theta) / (2* sin theta *cos theta)
= 25-144 / 120
=-119/120