Докажите тождество 1)sin2a-sin2a*cos2a=sin4a 2)sina/1+cosa+ctga=1/sina 1-2sin2a/2cos2a-1

((sina-cosa)^2-1+sin4a)/(cos2a+cos4a)=(sina^2-2sinacosa+cosa^2-sina^2-cosa^2+sin4a)/(cos2a+cos4a)=(-2sinacosa+sin4a)/ (cos2a+cos4a)=(-sin2a+2sin2a)/(cos2a+2cos2a)=

(sin2a(-1+2))/(cos2a(1+2)= sin2a/3cos2a=tg2a/3