Set P={x|2≤x≤5}
Q={x|k+ 1≤x≤2k- 1}
If P∩Q= empty set,
Discuss in two situations:
When q is an empty set, k+1>; 2k- 1, k<2. Satisfy the meaning of the problem.
When q is not an empty set, k+ 1≤2k- 1, k≥2.
There are k+ 1 > 5 or 2k- 1 < 2.
Then k > 4 or k < 3/2.
And because k≥2.
So k > 4.
To sum up, is k > 4 or K?