Given the complete set u = R, a = {X-2 ≤ x ≤ 5} B = {x M-1 ≤ x ≤ 2m + 1} if a ∩ B = &; find the range of M

Given the complete set u = R, a = {X-2 ≤ x ≤ 5} B = {x M-1 ≤ x ≤ 2m + 1} if a ∩ B = &; find the range of M

U = r a = {X - 2 ≤ x ≤ 5} B = {x M-1 ≤ x ≤ 2m + 1} if a ∩ B = & # 8709; then:
m-1＞5 m＞6
2m+1＜-2 m＜-3/2
So m range: M > 6 or m < - 3 / 2

The known set a = {X - 2 ≤ x ≤ 5}, B = {x m + 1 ≤ x ≤ 2m - 1}
A ∩ B = B, what is the value of M?
Wrong title=
A = {x ﹥ 15, or X ﹤ 5}, B = {x ﹥ m + 1 ≤ x ≤ 2m-1}
The answer is m < 3 or M > 14
But the teacher said that m ≤ 3 or ≥ 14
I don't understand

A = {X - 2 ≤ x ≤ 5}, B = {x m + 1 ≤ x ≤ 2m-1}
A ∩ B = B, that is, B is a subset of A
m+1>=-2
2m-1

If f (x) = log2 (x2-ax + 3a) increases monotonically in the interval [2, infinity], find the value range of real number a

F (x) = log2 (x2 ax + 3a) increases monotonically in the interval [2, infinity]
So the axis of symmetry x = A / 2 of G (x) = x & sup2; - ax + 3a is on the left side of the line x = 2 and G (2) > 0
So there are inequalities
a/20
The solution is - 4