Question

if sinx=3/5,cosy=12/13,where x and y both lie in 2nd quadrant, find the value of sin(x+y),cos(x-y),tan(x+y)?

Answer 1

in QII, cosy is negative
cosx = -4/5
siny = 5/13

now, just plug in the formulas. for example

sin(x+y) = sinx*cosy+cosx*siny
= (3/5)(-12/13)+(-4/5)(5/13)
= -36/65 - 20/65
= -56/65

Answer 2

-56/65