设等差数列{an}的公差为d ,且d>1.令bn=n2+nan,记Sn,Tn分别为数列{an},{bn}的前n项和.(1)若3a2=3a1+a3,S3+T3=21,
12.在等差数列{an}中,已知a1=1,公差d≠0,且a1,a2,a5成等比数列,数列{bn}的前n项和为Sn,b1=1,b2=2,且Sn+2=4Sn+3,n∈N*.(1)求an和bn;(2)设cn=an(bn-1),数列{cn}的前n项和为Tn,若(-1)nλ≤n(Tn+n2-3)对任意n∈N*恒成立,求实数λ的取值范围. 试题...
令y=f(x)= x2−x+n x2+x+1(x∈R,x≠ n−1 2,x∈N*),则y(x2+x+1)=x2-x+n,整理得:(y-1)x2+(y+1)x+y-n=0,△=(y+1)2-4(y-1)(y-n)≥0,解得: 3+2n−2 n2+1 3≤y≤ 3+2n+2 n2+1 3.∴f(x)的最小值为an= 3+2n−2 n2+1 3,最大值为bn= 3+2n+...