Đáp án:
`a) x^2y+xy-x-y=xy(x+y)-(x+y)`
`=(x+y)(xy-1)`
`b) ax^2-ay^2-7x-7y=a(x^2-y^2)-(7x+7y)`
`=a(x-y)(x+y)-7(x+y)`
`=(x+y)(ax-ay-7)`
`c) x^2+4x+3=x^2+x+3x+3`
`=x(x+1)+3(x+1)=(x+1)(x+3)`
`d) x^3-19x-30=x^3-5x^2+5x^2-25x+6x-30`
`=x^2(x-5)+5x(x-5)+6(x-5)`
`=(x-5)(x^2+5x+6)`
`=(x-5)(x^2+2x+3x+6)`
`=(x-5)(x+2)(x+3)`
`c) x^2-x-6=x^2-3x+2x-6`
`=x(x-3)+2(x-3)=(x-3)(x+2)`
`d) x^2-2x+1=(x-1)^2`
`e) 2y+1+y^2=(y+1)^2`
`g) 1+3x+3x^2+x^3=(1+x)^3`
`h) x+x^4=x(x^3+1)=x(x+1)(x^2-x+1)`