Math
posted by Jenn on .
Angle x is in the second quadrant and angle y is in the first quadrant such that sinx=5/13 and cosy=3/5, determine and exact value for cos (x+y).
I have no idea how to even start this question. Could someone please help me?

x=arcsin(5/13)
y=arccos(3/5)
so find those calculations and plug it into cos(x+y) or in other words
cos(x+y)=(arcsin(5/13)+arccos(3/5)) 
Well, I understand what you mean by the solution, but I am getting a really long decimal as the answer, so that's not an excat value. Please, can you help me some more?

Make diagrams of your triangles in the corresponding quadrants
if sinx = 5/13 and is in II
then cosx = 12/13
if cosy = 3/5 and is in I
then siny = 4/5
cos(x+y) = cosxcosy  sinxsiny
= (12/13)(3/5)  (5/13)(4/5)
= 56/65