Докажите тождество: а) (sint-cost)²=1-sin2t; б) 2cos²t=1+cos2t

а. (sint-cost)^2=1-sin2tsin^2 t-2sin t cos t +cos^2t t=1-sin 2tб. 2cos^2 t=1+cos2t1+cos 2t=sin^2 t+cos^2 t-sin^2 t+cos^2 t=2 cos^2 t