问题
填空题
若{an}是等差数列,公差d≠0,a2,a3,a6成等比数列,则公比为 ______.
答案
∵a2,a3,a6成等比数列,
∴a32=a2a6,即(a1+2d)2=(a1+d)(a1+5),整理得d2+2a1d=0
∴d=-2a1,
∴
=a3 a2
=a1+2d a1+d
=3-3d -d
故答案为3.
若{an}是等差数列,公差d≠0,a2,a3,a6成等比数列,则公比为 ______.
∵a2,a3,a6成等比数列,
∴a32=a2a6,即(a1+2d)2=(a1+d)(a1+5),整理得d2+2a1d=0
∴d=-2a1,
∴
=a3 a2
=a1+2d a1+d
=3-3d -d
故答案为3.