已知数列{an}满足an+1=qan+2q-2,(q为常数),若a3,a4,a5,a6∈{﹣18,﹣6,6,30},则a1=
问题描述:
已知数列{an}满足an+1=qan+2q-2,(q为常数),若a3,a4,a5,a6∈{﹣18,﹣6,6,30},则a1=
答
a6=q*a5+2q-2,a5=q*a4+2q-2,a4=q*a3+2q-2,a3=q*a2+2q-2,所以a6+2=q(a5+2),a5+2=q(a4+2),a4+2=q(a3+2),即a3+2,a4+2,a5+2,a6+2成等比数列,因a3,a4,a5,a6∈(-18,-6,6,30),所以a3+2,a4+2,a5+2,a6+2∈(-16,-4,8,32),q=-2,...