Problems on Factorization

Level1: Factorize the following (OR expand then factorize.) (2x-y)^2-(x+2y)^2 81a^4-256 (x-4)^2-18x Level2: Factorize the following. (OR expand then factorize) (a^2)(1+2b)+(b^2)(1+2a)+ab(2+ab) (a^2)(b+c)+(b^2)(a+c)+(c^2)(a+b)+2abc x^2+4x+xy+3y+3 (that seems easy.) Level X(？) List all pair (ax+b)(cx+d)=12x^2+ex+35(-1)^f that a-f is integer. Prove or disprove exist pair (a,c) that ax^2+bx+c can be factorize as (ex+/-f)(gx+/-h) While changing b. and a-g are a)Integers？ b)Reals？ c)Complex number？