Question

if cos(x) = 5/13 and sin(y) = 3/5 where 0<= x, y <= pi/2 determine:

a) cos(x+y)

b) sin(x - y)

c) sin2x

d) cos2y

Answer 1

so, sinx = 12/13
and cosy = 4/5
Now just apply the usual formulas. For example,
sin2x = 2 sinx cosx = 2(12/13)(5/13) = 120/169
You try the others. Post your work if you get stuck.