tana=sina/cosa=-2,sina=-2cosa(1)(sina+cosa)/(sina-cosa) =(-2cosa+cosa)/(-2cosa-cosa)=-cosa/-3cosa=1/3(2)tana=-2,sina=-2cosatan2a=sin2a/cos2a=2tana/(1-tan^a)=2*(-2)/(1-4)=4/3即sin2a=4/3cos2a=(4/3)(2cos^a-1)=(8/3)cos^a-4/3sinacosa=-2cos^a=1/2sin2a=1/2*[(8/3)cos^a-4/3]=(4/3)cos^a-2/3-2cos^a=(4/3)cos^a-2/3即(-10/3)cos^a=-2/3cos ^a=1/5故sinacosa=-2cos^a=-2/5