(cos15°sin9°+sin6°)/(sin15°sin9°-cos6°)=

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(cos15°sin9°+sin6°)/(sin15°sin9°-cos6°)=
(cos15°sin9°+sin6°)/(sin15°sin9°-cos6°)=

(cos15°sin9°+sin6°)/(sin15°sin9°-cos6°)=
原式=[cos15°sin9°+sin(15°-9)]/[sin15°sin9-cos(15°-9°)]
=(cos15°sin9+sin15°cos9°-cos15°sin9°)/(sin15°sin9°-cos15°cos9°-sin15°sin9°)
=sin15°cos9°/(-cos15°cos9°)
=sin15°/cos15°
=-tan15°
=-tan(45°-30°)
=-(tan45°-tan30°)/(1+tan45°tan30°)
=-2+√3
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