~ Bạn tham khảo ~
`a, (x+y)^3 - 1`
`= (x+y)^3 - 1^3`
`= (x+y-1)[(x+y)^2 + 1(x+y) + 1^2]`
`= (x+y-1)(x^2+2xy+y^2 + x + y + 1)`
`b, 100x^2-(x^2+25)^2`
`= (10x)^2 - (x^2+25)^2`
`= (10x-x^2-25)(10x+x^2+25)`
`= -(x^2-10x+25)(x^2+10x+25)`
`= -(x-5)^2(x+5)^2`