find the xact value of the expression. sin 200[] cos 80[] -cos 200[] sin 80[]?

Question

1. -10/3
2. sqrt[]3/2
3. -1/2
4. -sqrt[]3/2

Answer 1

From the trigonometric identities in the ref, SinAcosB - cosAsinB = sin(A-B), in this case sin(120 deg), which = +sqrt(3)/2. Answer 2.