1.x^2y(a-b)-xy(b-a)+y(a-b)

1.x^2y(a-b)-xy(b-a)+y(a-b)
=x^2y(a-b)+xy(a-b)+y(a-b)
=y(a-b)(x^2+x+1)
2.a^2n+a^(n+1)-a^n
=a^n*a^n+a*a^n-a^n
=a^n(a^n+a-1)
3.3a(m-n)-6b(n-m)-9c(m-n)
=3a(m-n)+6b(m-n)-9c(m-n)
=3(m-n)(a+2b-3c)
4.(3a+b)(3a-b)-(a+5b)(b-3a)
=(3a+b)(3a-b)+(a+5b)(3a-b)
=(3a-b)[(3a+b)+(a+5b)]
=(3a-b)(3a+b+a+5b)
=(3a-b)(4a+6b)
=2(3a-b)(2a+3b)