是 cos 10° cos 20° cos 30° = = = = = = = = =由积化和差公式,得cos 20° cos 10° = [ cos (20°+10°) +cos (20°-10°) ] /2= (cos 30° +cos 10°) /2,= √3 /4 +(1/2)cos 10°.所以 cos 10° cos 20° cos ...