It's six o'clock in the afternoon. It's time for 1！Jenny and Li Ming are2. Jenny's mother is 3 in the kitchen. Jenny and Li Ming help Mrs. Smith 4 the vegetables. After dinner, Mrs. Smith washes the 5 dishes. Li Ming dries the dishes.

已知tan（π+α）=﹣ $\frac{1}{2}$ ，求下列各式的值．

（Ⅰ）若f（x）无极值点，但其导函数f′（x）有零点，求a的取值；

（Ⅱ）若f（x）有两个极值点，求a的取值范围，并证明f（x）的极小值小于 $-\frac{1}{2}$ ．