Question 921229
sin u =5/13, cos u = -12/13   {{{13^2 - 5^2 = 144}}}, tan  u = -5/12
 and 
 cos v = −3/5, sin v = 4/5   {{{5^2 - 3^2 = 16}}}, tan v = -4/3
........
tan(u - v) =  (tan u -  tan v)/(1 + tan u tan v)
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