n 1+ 1+-+-1 n+ n+ l12(n+1)3!(n+1 n 2 十.+ (n+1)n+1八n+ n+ x <x 1-<1( n+1 x.<1++++.+一<1+1+-++-+.+ 2!3 2222 =1+ 2 <3 lim(1+-)10 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1! 2! 1 3! 1 1 1 1 2 ... 1 1 ... 1 1 ! 1 1 1 n n x n n n n n n n n n x x n n 1 n=1,2, 1 1 i=1,2, i n 2 3 1 1 1 1 1 1 1 1 1 1 1 ... 1 1 ... 1! 2! 3! ! 2 2 2 2 1 1- 2 1 =1+ 3 3 1 2 1 2 n n n n x n 1 lim(1 )n n e n