设un(x)(n=1,2,…)是[a,b]上的单调函数,证明:若∑un(a)与∑un(b)都绝对收敛,则∑un(x)在[a,b]上绝对且一致收敛.
设un(x)(n=1,2,…)是[a,b]上的单调函数,证明:若∑un(a)与∑un(b)都绝对收敛,则∑un(x)在[a,b]上绝对且一致收敛.
由于∑un(a)与∑un(b)都绝对收敛,即
当n>N时,对一切自然数p,有
而又由于un(x)在[a,b]上为单调函数,即有
因而
故由柯西准则知∑un(x)在[a,b]上绝对且一致收敛