1．和角公式sin(xy)=sinxcosycosxsiny(Sxy)cos(xy)=cosxcosy-sinxsiny(Cxy)tan(xy)=tanxtany/1-tanxtany(Txy)2．差角公式sin(x-y)=sinxcosy-cosxsiny(Sx-y)cos(x-y)=cosxcosysinxsiny(Cx-y)tan(x-y)=tanx-tany/1tanxtany(Tx-y)3.倍角公式sin2x=2sinxcosxcos2x=（cos^2）x-（sin^2）x=2（cos^2）x-1=1-2sin^2xtan2x=2tanx/1-（tan^2）xsin3x=3sinx-4（sin^3）xcos3x=4（cos^3）x-3cosxtan3x=3tanx-（tan^3）x/1-3（tan^2）x4.降幂公式（sin^2）x=1-cos2x/2（cos^2）x=i=cos2x/2PS：如果你还没学必修3的话（我告诉你＾是次方的意思，如X＾2就是2次方）
