数学题已知（sina+cosa)/(2sina-cosa)=2, sin^2a+3sinacosa+2cos^2a=?

日期：2014-12-28 10:21:20 人气：1

（sina+cosa)/(2sina-cosa)=2, （sina+cosa)=2(2sina-cosa) sina+cosa=4sina-2cosa sina=cosa sin^2a=cos^2a 因为sin^2a+cos^2a=1 则有sin^2a=1/2 sin^2a+3sinacosa+2cos^2a =sin^2a+3sinasina+2sin^2a =6sin^2a =6*1/2 =3