设各项均为正数的数列{an}的前n项和为Sn已知2a2=a1+a3数列{根号Sn}的公差为d的等差数列

{根号Sn}的公差为d的等差数列 √Sn=√S1+(n-1)d Sn=[√S1+(n-1)d ]^2=S1+(n-1)^2d^2+2√S1(n-1)dS2=S1+d^2+2√S1dS3=S1+4d^2+4√S1da1=S1a2=S2-S1= d^2+2√S1da3=S3-S2=3d^2+2√S1d2a2=a1+a3即2d^2+4√S1d=S1+3d^2+2...