Find the exact value of the trigonometric function

I really need some help with this problem, Midterms are a large portion of my grade.

Find the exact value of the trigonometric function that sin u = (-5/13), cos v (-3/5) and u and v are in Quadrant III.

tan(u - v) =

tan u = 5/12
tan v = 4/3
tan(u-v) = (tanu-tanv)/(1+tanutanv)
= (5/12-16/12)/(1+20/36)
= (-11/12)*36/56 = -33/56

sin v = -4/5
cos u = -12/13

tan(u - v) = sin(u - v) / cos(u - v)
= [sin(u)cos(v) - sin(v)cos(u)] / [cos(u)cos(v) + sin(u)sin(v)]
= (15/65 - 48/65) / (36/65 + 20/65)
= -23 / 56

Thomas...you SHOULD know 2 things...#1 tan ( u - v ) = { tan u - tan v } / { 1 + tan u tan v }

# 2 : angle u has point ( -12 , - 5 ) and angle v has point ( -3 , -4 )..so tangents can be found