Solution: ① When k=0, A={x|x∈R}, which obviously does not meet the meaning of the question, so k≠0.

(2) When k≠0, there are:

( 1):k & gt； 0

(2): △ = b 2-4ac ≤ 0, that is, k 2+8k ≤ 0.

From (1) and (2), k=?

To sum up, there is no k value that makes A=?

PS: I don't know how to set the topic, which gives me the feeling that there is something wrong with the topic.