Sin(21)0 cos(9)0 - cos(84)0 cos(6)0
\({\color{blue}sin 21°cos9°-sin84°cos6°}\)
\({\color{blue}= 0.3584\times0.9877-0.9945\times0.9945}\)
\({\color{blue}= -0.635117954957}\)
!
!
