BnAn-B[n+1]A[n+1]≥δA[n+1]>0,则正项数列{AnBn}单调减,故收敛,即级数∑BnAn-B[n+1]A[n+1]收敛.而δ An≤(BnAn-B[n+1]A[n+1]),由比较判别法∑An 收敛 .
采纳是一种美德!