听短文填空。 What Susan is interested in 1.__________. What Traveling is 2.__________. in her life. When This 3.__________, her family are coming to China. How long They will stay here for 4.__________. How Then they will 5.__________ to Beijing.
【简答题】已知函数f(x)=x+ a x 的定义域为(0,+∞),a>0且当x=1时取得最小值,设点P是函数图象上的任意一点,过点P分别作直线y=x和y轴的垂线,垂足分别为M、N. (1)求a的值; (2)问:PM?PN是否为定值?若是,则求出该定值,若不是,请说明理由; (3)设O为坐标原点,求四边形OMPN面积的最小值.