lim [f(x)+g(x)]=lim[(A+B)+(α+β)]
=lim(A+B)+lim(α+β)
=A+B+0
=A+B
所以lim [f(x)+g(x)]=lim f(x)+lim g(x)
注:无穷小的和仍是无穷小,极限仍等于零.