1,n/(n^2+156)的最大值,y=x/(x^2+156)=1/(x+156/x)≤1/(2√156)=1/(4√39),当x=156/x即x=2√39时等号成立,12＜2√39＜13所以最大值为n=12或13时出现,n=12时,n/(n^2+156)=12/300=0.04n=13时,n/(n^2+156)=13/325=0.04...