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?
so find those calculations and plug it into cos(x+y) or in other words
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)