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课后达标检测
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1.cos 260°=( )
A.-cos 10° B.cos 10°
C.-sin 10° D.sin 10°
解析:cos 260°=cos (360°-100°)=cos (-100°)=cos 100°=cos (10°+90°)=-sin 10°.故选C.
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课后达标检测
解析:sin (2 025π-α)=sin (2 024π+π-α)=sin (π-α)=sin α,故A正确;
tan (α-2 024π)=tan α,故B错误;
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课后达标检测
解析:对于A,cos (A+B)=cos(π-C)=-cos C,故A正确;
对于B,tan (B+C)=tan (π-A)=-tan A,故B错误;
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13.cos21°+cos22°+cos23°+…+cos289°=________.
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