tan(π/4+a)=(tan(π/4)+tana)/(1-tan(π/4)*tana)=(1+2)/(1-2)=-3[sina2a+cos^2(π-a)]/(1+cos2a)=[2sina*cosa+cos^2a]/(sin^2a+cos^2a+cos^2a-sin^2a)=(2sina*cosa+cos^2a)/2cos^2a(上下同除以cos^2a)=(2tana+1)/2...