你题目抄错啦,最后应该是f(2/n)
解:
lim(n->∝)√n*√f(2/n)
=lim(n->∝)√2 *√[f(2/n)/(2/n)]
=√2lim(n->∝)√f(2/n)/(2/n)
n->∝,2/n->0, u=2/n
=√2lim(u->0)√[f(u)/u]
f'(u)|u=0 =lim(u->0)f(u)/u
y=sinx,y'=cosx
f'(x)|x=0=cos0=1, lim(u->0)f(u)/u=1
lim(n->∝)√n*√f(2/n)=√2lim(u->0)√[f(u)/u]=√2
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