A friend of mine named Paul received an expensive car from his brother as a Christmas present．On Christmas Eve when Paul came out of his office, a street urchin （顽童）was walking around the
A warm smile on the street, a happy “hello” in a public park or the cheery sound of your name at the neighborhood bar — it doesn’t take much to feel at home in a busy city. And in the follo
满足
,若直线
将可行域分成面积相等的两部分，则实数
的值为______. 
