So: a? -a+ 1=3 or a

Solve the equation: a=- 1 or 2 or 1. Substitute a into the set and verify that a= 1 is invalid.

So a=- 1 or 2.

2: x-a < 0, so: x < a.

Because; A is indeed contained in B, so: X < A contains a range greater than 1 < X < 2 (it can be turned into a number axis).

So; a≥2

Question 3: For Scheme A, x= 1 or x=2,

Because: b is contained in a.

Therefore, if x= 1 or x=2 in set b is substituted into b, a= 1 or a=2 is obtained.

When b is an empty set:

△=4-4(a- 1) 2 (Thanks for scoring! )