lg3x+lgy=lg(x+y+1)lg3xy=lg(x+y+1)3xy=x+y+1 x>0 y>03xy=x+y+1>=2√xy+13xy-2√xy-1>=0(3√xy+1)(√xy-1)>=0√xy<=-1/3(舍去) √xy>=1 xy>=1所以xy最小值是1x+y+1=3xy>=3x+y>=2所以x+y的最小值是2
