an+an+2 |
2 |
an+2−an+1 |
n+2−n−1 |
an+1−an |
n+1−n |
∴
a10−a1 |
10−1 |
a5−a1 |
5−1 |
在|an-bn|≤20,bn=n2-6n+10中,令n=5,得b5=25-30+10=5,
∴-20≤a5-b5≤20,∴-15≤a5≤25…(2).
(1)、(2)联立得13≤a≤25.
答案:[13,25].
f(x1)+f(x2) |
2 |
x1+x2 |
2 |
an+an+2 |
2 |
an+an+2 |
2 |
an+2−an+1 |
n+2−n−1 |
an+1−an |
n+1−n |
a10−a1 |
10−1 |
a5−a1 |
5−1 |