cot a/2-tan a/2=cos(a/2)/sin(a/2)-sin(a/2)/cos(a/2)=cosa/[sin(a/2)cos(a/2)]=2cosa/sina所以:(1+cos2a)/(cot a/2-tan a/2)=(1+2(cosa)^2-1)/(2cosa/sina)=sinacosa又因为sina+cosa=2/3那么有:(sina+cosa)^2=1+2s...