Decide True or False: The author Qu Yuan is a great poet and the first writer to have his name associated with his work in the history of Chinese literature.
【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.