sin6°cos24°•sin78°cos48°的值等于 A.- 1/16 B.- 1/8 C.1/16 D.1/8

sin6°cos24°=(1/2)*(sin30°+sin18°)sin78°cos48°=(1/2)*(sin30°+sin126°)=(1/2)*(sin30°+sin54°)(根据和差化积公式.)所以原式=(1/4)*(1/2+sin18°)*(1/2+sin54°)=(1/4)*[1/4+(1/2)*(sin18°+sin54°)+sin...