y=x+1/x-3=x-3+1/(x-3) +3 因为x>3,所以: y=x+1/x-3=x-3+1/(x-3) +3=[√(x-3) - 1/√(x-3)]^2 +2 +3>=5 当√(x-3) - 1/√(x-3)=0 ,即x=4时,y有最小值5.
