444.2a] `x^3+x=x(x^2+1)`
444.2b] `xy-7y=y(x-7)`
444.2c] `a-ab=a(1-b)`
444.2d] `x+2x=x(1+2y)`

444.7a] `3a^2b-ab^2+abc=ab(3a-b+c)`
444.7b] `2a^3b-4a^2b^2+4ab^3=2ab(a^2-2ab+2b^2)`
444.7c] `-2ab^3+2a^2b-6a^2b^2=2ab(-b^2+a-3ab)=2ab(a-3ab-b^2)`

444.16a]
`5(5x+2y)^4+25(5x+2y)^3x=`
`=5(5x+2y)^3[(5x+2y)+5x]=`
`=5(5x+2y)^3[10x+2y]=`
`=10(5x+2y)^3(5x+y)=`

444.16b]
`ax(x^2+y^2)+ax^2(x+y)=`
`=ax^3+axy^2+ax^3+ax^2y=`
`=2ax^3+axy^2+ax^2y=`
`=ax(2x^2+y^2+xy)`