(1)求A1, A2
(2)设bn=An+2,证明数列{bn}是等比数列,并指出其首项和公比
2.已知数列{An}满足A1=-1,An+1=2An,求该数列前十项的和S10
(1)求A1, A2
(2)设bn=An+2,证明数列{bn}是等比数列,并指出其首项和公比
2.已知数列{An}满足A1=-1,An+1=2An,求该数列前十项的和S10
(1) a1=1 a2=2*a1+2=4
(2)an=2的(n-1)次方+2的n次方-2 bn=2的(n-1)次方+2的n次方=3*2的(n-1)次方
所以bn是以3为首项,以2为公比的等比数列
(3) an=-(2的(n-1)次方)
S10=-(1+2+4+ 2的九次方)=1-2的十次方