m=(x2+3x+6)/(x+2)= [ (x^2 + 4x + 4) -(x +2) + 4] / (x+2)= [ (x+2)^2 - (x+2) + 4]/(x+2)= (x+2) + 4/(x+2) - 1>= 2√[(x+2) * 4/(x+2)] - 1= 3当且仅当 (x+2) =4/(x+2) ,即x = 0时,取得最小值