A= 1/3 or-1/2 or 0; (Pay special attention to the case of a=0, an empty set is a subset of any set)

0;

m；

Solution: according to (CuA)∩B={2}, A∩(CuB)={4}

It is known that 2 is an element of set B and 4 is an element of set A; And 2 is not an element of set A, and 4 is not an element of set B.

Substitute 4 and 2 into set A\B to get the equation:

16+4a+ 12b=0

4-2a+b=0

Get: a=8/7 b=- 12/7.

Solution: According to the meaning of the question, x 2-4mx+2m+6 = 0 has at least one solution less than 0.

△ = 16m 2-4 (2m+6) ≥ 0m ≥ 3/2 or m≤- 1.

x 1=2m+√(4m^2-2m-6)x2=2m-√(4m^2-2m-6)

Obviously x2≤x 1

So there are: 2m-√ (4m 2-2m-6)

When m≥3/2, solve the above formula to get: m.

When m≤- 1, the above formula holds.

To sum up: m≤- 1

Solution: b: x 2-5x+6 = 0x = 2 or x=3.

C: x 2+2x-8 = 0x = 2 or x=-4.

B∩C={2}=A∩B

That is, 2 is an element of the set A. If it is substituted into the equation, it is: a 2+2a+15 = 0.

No solution! ! ! The landlord must have copied the equation of group A wrong. I estimate that the topic is a = {x | x 2-ax+a 2- 19 = 0}.

Solution: Suppose there are X netizens who agree with A and B, and x/3+ 10 netizens who disagree with A and B.

The number of people in favor of A =500*3/5=300; the number of people who disapprove of A =200.

Number of people in favor of B =300+30=330 Number of people who disapprove of B 170

So: the number of people who only agree with A =300-x, and the number of people who only agree with B = 330-x.

The number of people who disapprove of both A and B = 500-(300-x+330-x+x) = x-130.

So there are: x-130 = x/3+10x = 210.

A: There are 2 10 netizens who agree with A and B, and 80 netizens who disagree with A and B..