posted by Anonymous .
If sinx=3/5,cosy=-12/13,where x and y both lie in 2nd quad.Find the value os sin(x+y).
luckily, you have nice easy 3-4-5 and 5-12-13 triangles.
cosx = -4/5
siny = 5/13
sin(x+y) = (3/5)(-12/13) + (-4/5)(5/13) = -56/65
reasonable, since (x+y) will be in QIII or QIV