Đáp án:
`x^2(x^2-6)-x^2+9`
`= x^4-6x^2-x^2+9`
`= (x^4-6x^2+9)-x^2`
`= [(x^2)^2-2xx x^2 xx3+3^2]-x^2`
`= (x^2-3)^2-x^2`
`= (x^2-3-x^2)(x^2-3+x^2)`
`= (-3)xx(2x^2-3)`
$\\$
`(x^2+4y^2-5)^2-16(x^2y^2+2xy+1)`
`= (x^2+4y^2-5)^2-16(xy+1)^2`
`= (x^2+4y^2-5)^2-[4(xy+1)]^2`
`= [x^2+4y^2-5-4(xy+1)][x^2+4y^2-5+4(xy+1)]`
`= [x^2+4y^2-5-4xy-4][x^2+4y^2-5+4xy+4]`
`= [(x^2-4xy+4y^2)-9][(x^2+4xy+4y^2)-1]`
`= [(x-2y)^2-3^2][(x+2y)^2-1^2]`
`= (x-2y-3)(x-2y+3)(x+2y-1)(x+2y+1)`