Đáp án:
`4. =x(x-y)+(x-y)=(x-y)(x+1)`
`5. =x(a-b)-(a-b)^2=(a-b)(x-a+b)`
`6. =(x^2+4x+4)-y^2=(x+2)^2-y^2=(x+2+y)(x+2-y)`
`7. =x^2(x-1)-(x-1)=(x-1)(x^2-1)=(x-1)(x-1)(x+1)=(x-1)^2(x+1)`
`8. =(x^2+3y)^2-1=(x^2+3y+1)(x^2+3y-1)`
`9. =(a+b)^2-c(a+b)=(a+b)(a+b-c)`
`10. =x^2(y-x)-9(y-x)=(y-x)(x^2-9)=(y-x)(x+3)(x-3)`