x→0时,令y=x+[√(1+x²)-1]则lim(x→0) [y/x]=lim(x→0) [x+[√(1+x²)-1]] / x=lim(x→0) [1+[√(1+x²)-1]/x]=1+lim(x→0) [√(1+x²)-1]/x=1+lim(x→0) [0.5x²]/x=1+lim(x→0) [0.5x]=1+0=1由等价无穷小的定义，若lim(x→0) [y/x]=1则y与x为等价无穷小
