求值：sin21°cos81°-sin69°cos9°
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求值：sin21°cos81°-sin69°cos9°求值：sin21°cos81°-sin69°cos9°求值：sin21°cos81°-sin69°cos9°sin21cos81-sin69cos
求值：sin21°cos81°-sin69°cos9°
求值：sin21°cos81°-sin69°cos9°
求值：sin21°cos81°-sin69°cos9°
sin21cos81-sin69cos9
=-sin21sin69cos81cos9
=[-sin21cos(90-69)][sin(90-81)cos9]
=(-sin21cos21)(sin9cos9)
=-(1/2sin42)(1/2sin18)
=-1/4sin42sin18
额,后面的忘了,自己算算吧,翻翻书,有这种类型的解法的.
sin21°cos81°-sin69°cos9°
=sin21°sin9°-cos21°cos9°
= - cos30°
=-√3/2
求值：sin21°cos81°-sin69°cos9°
sin21°cos81°-cos21°sin81°=?
sin21°cos81°-sin69°cos9°
sin21°cos81°+cos189°sin69°化简
sin21°cos81°+sin69°cos9°化简要详解
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sin21度cos81度-sin69度cos9度=?
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