x趋近于0时 x^(1/3)+x^(3/4)是x的几阶无穷小?解：由于x➔0lim[(x^(1/3)+x^(3/4)]/x^(1/3)]=x➔0lim{x^(1/3)[1+x^(5/12)]/x^(1/3)}=x➔0lim[1+x^(5/12)]=1，∴x➔0时x^(1/3)+x^(3/4)是x的1/3阶无穷小。或者说x^(1/3)+x^(3/4)与x^(1/3)是等价的无穷小。
