Question

已知an=1/(n+1)+1/(n+2)+1/(n+3)+...+1/2n,求证:当n大于等于3时

已知an=1/(n+1)+1/(n+2)+1/(n+3)+...+1/2n,求证:当n大于等于3时，an＞3/5

Answer 1

先证明an+1-an恒大于0，得到an递增。当n>=3时，an>=a3........估计差不多了。