Ալեն Ավետիսյան

sin2a/sina=2sina*cosa/sina=2cosa sin2a/cos2a=2sinacosa/2cos2a=sina/cosa=tga sin2a/sina-cosa=2sina*cosa/sina-cosa=2cosa-cosa=cosa cos2a-cos2a=cos2a-sin2a-cos2a=-sin2a sin2a+cos2a=sin2a+cos2a-sin2a=cos2a sin2a-cos2a=-(cos2a-sin2a)=-cos2a 2sinπ/12*cosπ/12=sin(2*π/12)=sinπ/6=1/2 cos²15°-sin²15°=cos(2*15)=cos30°=√3/2