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°的值为用到的公式:[cos(180°+
sin21°cos189°-sin69°sin9°的值为
sin21°cos189°-sin69°sin9°的值为
sin21°cos189°-sin69°sin9°的值为
用到的公式:[cos(180°+A)=-cosA/sin(90°-A)=cosA/sin(A+B)=sinAcosB+cosAsinB]
因为cos189°=cos(180°+9°)=-cos9°
和sin69°=sin(90°-21°)=cos21°
所以
sin21°cos189°-sin69°sin9°
=-sin21°cos9°-cos21°sin9°
=-(sin21°cos9°+cos21°sin9°)
=-sin(21°+9°)
=-sin30°
=-(1/2)
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用诱导公式和两角和的正弦公式得出-1/2
根据诱导公式，
角度制下的角的表示：
sin（180°+α）=－sinα
cos（180°+α）=－cosα
tan（180°+α）=tanα
角度制下的角的表示：
sin (90°－α)=cosα
cos (90°－α)=sinα
tan (90°－α)=cotα
sin21°cos189°-sin69°sin9°=-sin21cos9-cos21sin9=-sin30=-1/2
原式=sin（90°-69°）cos（180°+9°）-sin69°sin9°=cos69°（-cos9°）-sin69°sin9°=-（cos69°cos9°+sin69°sin9°）=-cos（69°-9°）=-cos60°=-1/2
sin21°cos81°+cos189°sin69°化简
sin21°cos189°-sin69°sin9°的值为
sin21°cos189°-sin69°sin9°的值为
sin21°cos81°-sin69°cos9°
求值：sin21°cos81°-sin69°cos9°
sin21°cos81°+sin69°cos9°化简要详解
cos24°cos69°-sin24°sin69°等于多少
sin21度cos81度-sin69度cos9度=?
(sin39° -sin21°)/(cos39°-cos21°)
sin21°cos39°+cos21°sin39°=
sin21°cos24°+cos21°sin24°
sin21°cos81°-cos21°sin81°=?
求值sin21°cos24°+cos21°sin24°过程
求值sin21°cos24°+cos21°sin24°过程
sin21°cos9°+cos21°sin9°=?
求sin21°+sin22°+...+sin289°的值.
求值：sin21/4π tan(-23/6π) cos1500°
(sin24°cos6°-sin66°sin6°)/(sin21°cos39°-cos21°sin39°)