2+sinacosa-cos^2a=2(sin^2a+cos^2a)+sinacosa-cos^2a=2sin^2+sinacosa+cos^2a=[2sin^2a+sinacosa+cos^2a]/(sin^2a+cos^2a)=(2tan^2a+tana+1)/(tan^2a+1),(分子分母同除以cos^2a)=(2*9/16-3/4+1)/(1+9/16)=22/25
