1) =a^4+b^4-a^4+a^2*b^2=b^2(b^2+a^2)
2)=m^2+m*n-m^2+n^2=n(m+n)
3)=(12x^2+6x)*((5y+7z)+(7z-5y))=6*(2x^2+x)*(5y+7z+7z-5y)=6*(2x^2+x)*14z
4)=(5y-7z)*((12x^2-6X)+(12x^2+6X))=(5y-7z)*(12x^2-6x+12x^2+6x)=24x^2*(5y-7z)
5)=(3a^2-2b)*(5x+3y)-(2b-3a^2)=(3a^2-2b)(5x+3y+1)
6)=(4a-7b)(5a-8b-1)
7)(x^2-x-1)((y+2)-(z+12))
8)(2k^2-3m)((y^2-y+2)-(y-y^2-2))=(2k^2-3m)(2y^2-2y+4)