tan(π/4+α)=(1+tana)/(1-tana)=2tana=1/3cosa=3sinasin^2a+cos^2a=1 a为锐角sina=√10/10 cosa=3√10/10sin2a=2sinacosa=3/5 cos2a=cos^2a-sin^2a=4/5(sin2αcosα-sinα)/cos2α=(3/5*3√10/10-√10/...