Question

Find the exact value of sin(x+y) when sinx=-1/4 and cosy=-3/5 in q2

Answer 1

sin (x + y) = sin x cos y + sin y cos x

sin y = -4/5  and cos x = -sqrt255

so sin(x + y) =  -1/4 * -3/5 + -4/5 * sqrt255
                    = 3/20 - 4 sqrt255/5
                    = (3 - 16 sqrt255) / 20   answer