Scaling method, first amplification, is except k/n, so the denominator is n+k, so the original formula =limn? [k/n-k/(n+k)]

=limn？ k？ /n(n+k)=k？

Narrowing, that is, the denominator behind becomes n+ 1, then the original formula =limn? [k/n-k/(n+ 1)]=limn？ nk/n(n+ 1)

=limn？ K/(n+ 1), I feel that I can't get it anymore.