Đáp án + giải thích các bước giải:
a) `x^2-x-6`
`=x^2-3x+2x-6`
`=x(x-3)+2(x-3)`
`=(x+2)(x-3)`
b) `x^4+4x^2-5`
`=x^4-x^3+x^3-x^2+5x^2-5x+5x-5`
`=x^3(x-1)+x^2(x-1)+5x(x-1)+5(x-1)`
`=(x^3+x^2+5x+5)(x-1)`
`=[x^2(x+1)+5(x+1)](x-1)`
`=(x^2+5)(x+1)(x-1)`
c) `x^2-19x-30`
`=x^2-2.x .19/2 +361/4-481/4`
`=(x-19/2)^2-481/4`
`=(x-19/2-\sqrt{481}/2)(x-19/2+\sqrt{481}/2)`
d) `x^4+x^2+1`
`=x^4+x^3+x^2-x^3-x^2-x+x^2+x+1`
`=x^2(x^2+x+1)-x(x^2+x+1)+x^2+x+1`
`=(x^2-x+1)(x^2+x+1)`
