2、{ 2 & ltx & lt3}

3，{ k/-3 & lt； k & lt0}

4,(- 1,- 1)

5, A5, B2, at least 1304.

6. The minimum circumference under the root number S is four times that under the root number S..

7,4 p is the square of p, and the maximum area is16 p.

8 Speed is B, ab has the lowest cost, and ab is 2s times.