1.)当n=2时原式=1/3+1/4+1/5+1/6=57/60 >5/62.)假设当n=k时,（k为任意大于2的数）存在1/(k+1）+1/(k+2)+1/(k+3)+…+1/3k ＞5/63.)所以,当n=k+1时原式=1/(k+2）+1/(k+3)+1/(k+4)+…+1/3k+1/(3k+1)+1/(3k+2)+1/(3k+3)...