cos72cos12+sin72sin12
cos72度 cos12度+sin72度sin12度的值是多少? -
=cos(72-12)=cos60 =1/2
=cos(72-12)=cos60 =1/2
=cos(72-12)=cos60 =1/2
=cos(72-12)=cos60 =1/2
=cos(72-12)=cos(60)=1/2
cos（72-12）cos60 公式要记牢：cos(a+b)=cosacosb-sinasinb cos(a-b)=cosacosb+sinasinb
cos72度cos12度+sin72度sin12度 -
cos72度cos12度+sin72度sin12度=sin18度cos12度+cos18度sin12度=sin(18度+12度）sin30度=1/2
cos(A-B)=cosAcosB+sinAsinB。。。所以原式=cos( 72度-12度）cos60度=0.5
sin18°sin78°+sin72°sin12°=(要过程) -
原式=cos(90-18)cos(90-78)+sin72sin12 =cos72cos12+sin72sin12 =cos(72-12)=cos60 =1/2
cos72(cos72－cos12)＋sin72(sin72－sin12）=[(cos72)^2+(sin72)^2]-(cos72cos12+sin72sin12) =1-cos60 =1/2
化简cos72°sin78°+sin72°sin12°等于? -
cos72°sin78°+sin72°sin12° =cos72°cos12°+sin72°sin12°（sinα=cos（90°-α））cos（72°-12°）（和角公式cos（α-β）cosαcosβ+sinαsinβ）cos60°=1/2
在单位圆上啊，
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