已知{an}为等差数列,且a3=-6,a6=0(1)求0000000000000000000000000000000000000000000
问题描述:
已知{an}为等差数列,且a3=-6,a6=0(1)求0000000000000000000000000000000000000000000
已知{an}为等差数列,且a3=-6,a6=0
(1)求{ |an| }的前n项和;
(2)若等差数列{bn}满足b1=-8,b2=a1+a2+a3,求{bn}|前n项和公式.
答
(1)因为,a6=a3+3d所以,3d=0+6=6d=2又,a3=a1+2d所以,a1=a3-2d=-6-4=-10等差数列通项为an=-10+2(n-1)=2n-12n=6时,an=0n0数列{an}的前n项和=(-10+2n-12)n/2=n(n-11)数列{an}的前6项和=(-10+0)×6/2=-30所以,n≤6...