sin21°cos189°-sin69°sin9°的值为

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sin21°cos189°-sin69°sin9°的值为
sin21°cos189°-sin69°sin9°的值为

sin21°cos189°-sin69°sin9°的值为
sin21°cos189°-sin69°sin9°
=-sin21°cos9°-cos21°sin9°
=-(sin21°cos9°+cos21°sin9°)
=-sin(21°+9°)
=-sin30°
=-1/2

sin21°cos189°-sin69°sin9°
=-sin21°cos9°-cos21°sin9°
=-(sin21°cos9°+cos21°sin9°)
=-sin(21+9)°
=-1/2