<span><span>(sin^t+2sintcost-cos^2t)^2=(sin2t-cos2t)^2=(sin2t)^2+(cos2t)^2-2sin2tcos2t=1-sin4t 1 - cos альфа + cos 2альфа / sin 2альфа - sin альфа= =(1-cosa+2cos^2a-1)/(sina(2cosa-1)=cosa(2cosa-1)/sina(2cosa-1)=cosa/sina=ctga </span>sin 5пи/18 cos пи/9 - sin пи/9 cos 5пи/18 / sin 5пи/12 sin 7пи/12 - cos 5пи/12 cos 7пи/12= =sin(5pi/18-2pi/18)/-(cos(5pi/12+7pi/12)=sin(pi/6)/-cospi=1/2 </span>