温馨提示： 此套题为Word版，请按住Ctrl,滑动鼠标滚轴，调节合适的观看比例，答案解析附后。关闭Word文档返回原板块。课堂检测素养达标1.cos 20=()A.cos 30cos 10-sin 30sin 10B.cos 30cos 10+sin 30sin 10C.sin 30cos 10-sin 10cos 30D.cos 30cos 10-sin 30cos 10【解析】选B.cos 20=cos(30-10)=cos 30cos 10+sin 30sin 10.2.cos(-35)cos(25+)+sin(-35)sin(25+)的值为()A.-B.C.-D.【解析】选B.原式=cos(-35)-(+25)=cos60=.3.已知cos =,则cos=_.【解析】因为cos =,所以sin =.所以cos=cos cos +sin sin=+=.答案:【新情境新思维】已知sin +sin +sin =0,cos +cos +cos =0,求证:cos(-)=-.【证明】由sin +sin +sin =0,cos +cos +cos =0得(sin + sin )2=(-sin )2,(cos +cos )2=(-cos )2.+得,2+2(cos cos +sin sin )=1,即2+2cos(-)=1,所以cos(-)=-.关闭Word文档返回原板块
