1.4x ∧4-21x ²+1
2.x ²-6x-y ²-4y+5
3.x ²-4xy+4y ²-2x+4y-35
4.(x ²+x-2).(x ²+x-3)+12
5.(x+4).(x+6).(x+6).(x+10)+128
1.4x ∧4-21x ²+1
2.x ²-6x-y ²-4y+5
3.x ²-4xy+4y ²-2x+4y-35
4.(x ²+x-2).(x ²+x-3)+12
5.(x+4).(x+6).(x+6).(x+10)+128
`1)4x^4-21x ²+1`
`=4x^4+4x^2-25x^2+1`
`=(2x^2+1)^2-(5x)^2`
`=(2x^2+5x+1)(2x^2-5x+1)`
`2)x ²-6x-y ²-4y+5`
`=x^2-6x+9-y^2-4y-4`
`=(x-3)^2-(y+2)^2`
`=(x-y-5)(x+y-1)`
`3)x ²-4xy+4y ²-2x+4y-35`
`=(x-2y)^2-2(x-2y)-35`
`(x-2y)^2-2(x-2y)-35`
$\text{Đặt: x – 2y = z}$
`⇒z^2-2z-35`
`=z(z-7)+5(z-7)`
`=(z+5)(z-7)`
$\text{Quay trở lại ta có:}$
`⇒(x-2y+5)(x-2y-7)`
$\text{Câu 4, 5 b xem lại đề ;-;}$
Đáp án:
1) 4x^4 -21x² +1
= 4x^4 +4x² +1-25x²
=(2x² +1)² -(5x)²
=(2x²+1-5x).(2x²+1+5x)
2)x² -6x -y²-4y +5
=x² -6x -y²-4y +9-4
=(x² -6x +9) -(y² +4y+4)
=(x-3)² -(y+2)²
=(x-3 -y-2).(x-3+y+2)
=(x-y-5).(x+y-1)
3)x² -4xy +4y² -2x +4y -35
=(x-2y)² – 2.(x -2y) +1 -36
=(x-2y -1)² -6²
=(x-2y-1 +6).(x-2y-1 -6)
=(x-2y+5).(x-2y -7)
phần 4;5 mình thấy hới sai bạn xem lại .