Докажите тождество
1)sina-sin3a/cosa-cos3a=-ctg2a
2) 2tga/1-tg^2a (cos^2a-1)=sin2a
1)sina-sin3a/cosa-cos3a=-ctg2a
2) 2tga/1-tg^2a (cos^2a-1)=sin2a
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Sina-sin3a/cosa-cos3a=-ctg2a2sin(-a)cos2a/(-2sin(-a)sin2a)=-2sinacos2a/(2sinasin2a)=-cos2a/sin2a=
=-ctg2a
-ctg2a=-ctg2a