1.tana=2则(sina-2cosa)/(4cosa+sina)分子、分母同时除以cosa得(sina-2cosa)/(4cosa+sina)=(tana-2)/(4+tana)=02.2sin^2a+sinacosa-3cos^2a=(2sin^2a+sinacosa-3cos^2a)/1=(2sin^2a+sinacosa-3cos^2a)/(sin^2a+cos^2...