3x+2y>=2√(6xy) 12>=2√(6xy) √(6xy)<=6 6xy<=36 xy<=6 xy的最大值为6 1/x+1/y=(x+y)/xy x+2y/3=4 y+3x/2=6 x+y+2y/3+3x/2=10 x+y=10-(3x/2+2y/3)<=10-2√xy<=10-2√6 （x+y）/xy>=(10-2√6)/6=5/3-√6/3 1/x+1/y的最小值为5/3-√6/3
