数列各项均为正,Sn>0.2√Sn是a(n+2)与an的等比中项,则(2√Sn)²=(an+2)an4Sn=an²+2ann=1时,4a1=4S1=a1²+2a1a1²-2a1=0a1(a1-2)=0数列各项均为正,a1>0,因此只有a1-2=0a1=2n≥2时,Sn=(an²+2an)...