Question

Sin(-330).cos(-300)+sin(-420).cos390 =-1/2

Answer 1

Sin(-x)=Sin(360-x),Sin(90-x)=Cos(x) so
Sin(-330)=1/2;Cos(-300)=1/2;Sin(-420)=-Sin60;Cos390=Cos30=Sin60
So
1/2×1/2-3/4=-1/2