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?

Math 
stephanie,
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)) 
Math  I still don't understand 
Jenn,
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?

Math 
Reiny,
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