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