log3(xy)=2xy=99(1/x+1/y)=xy(1/x+1/y)=x+y≥2√xy=6所以最小值=6/9=2/3
即log(9xy)=2xy=100/91/x+1/y >= 2/(xy)^1/2当且仅当x=y所以 >= 2/(100/9)^1/2 = 3/5 当且仅当x = y = 10/3时成立
log(3)[x]+log(3)[y]=2log(3)[xy]=2则:xy=3²=91/x+1/y≥2√[1/(xy)]=2/3即:1/x+1/y的最小值是2/3