已知数列{an}中,a1=1,a2=0,对任意正整数n,m(n>m)满足a2n−a2m=an−man+m,则a119=_.

问题描述:

已知数列{an}中,a1=1,a2=0,对任意正整数n,m(n>m)满足

a 2n
a 2m
an−man+m,则a119=______.

令n=2,m=1,则(a22-(a12=a1a3
因为a1=1,a2=0,所以a3=-1;
令n>2,m=2,则(an2-(a22=an-2an+2
所以

an+2
an
an
an−2

所以
a119
a117
a117
a115
=…=
a3
a1
=-1
所以
a119
a1
=(
a3
a1
)
59
=-1;
所以a119=-a1=-1