数学归纳法即得。
by Feng_Jing @ 2022-06-13 11:50:26
$f_{n+2}=f_{n+1}+f_{n}$
$f_{n+1} =f_{n}+f_{n-1}$
$...$
$f_3=f_2+f_1$
联立得：
$\sum_{i=3}^{n+2}f_i=f_1+2\sum_{i=2}^{n}f_i+f_{n+1}$
$\sum_{i=3}^{n+2}f_i=\sum_{i=1}^n f_i+\sum_{i=2}^{n+1}f_i$
$f_{n+2}-f_2=\sum_{i=1}^n f_i$
by ningago @ 2022-06-13 12:00:39
@[GoLover](/user/687374)
by ningago @ 2022-06-13 12:01:10
@[ningago](/user/371968)
by GoLover @ 2022-06-13 12:25:58
@[GoLover](/user/687374) （4，3）应为b
by felixesintot @ 2022-08-19 20:42:43
@[mushvase](/user/289608)
握靠，那下面的也好像都错了o(╥﹏╥)o
by GoLover @ 2022-08-20 20:05:56