1sina=12/13cosa=-√(1-sin²a)=-√(1-144/169)=-√)25/169)=-5/13tga=sina/cosa=12/13:(-5/13)=-12/13*13/5=-12/5ctga=1/tga=1:(-12/5)=-5/122cos9π/4=cos(2π+π/4)=cosπ/4=√2/23tg²a*(1+cos2a)-sin²a=sin²a/cos²a*2cos²a-sin²a=2sin²a-sin²a=sin²a6cos²π/12-sin²π/12=cos(2*π/12)=cosπ/6=√3/281-sin2a=sin²a+cos²a-2sinacosa-(sina-cosa)²9(1-sin2a)/(ctga*tga-25sinacosa)=(1-sin2a)/(1-sin2a)=1