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a, 2xy^2 ( x^3 -3xy - 4 )
b, x^2 - 4x - 4x +16
= x(x-4) - 4(x-4)
= (x-4) (x-4)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(x^4+8x+63\)
\(=x^4+4x^3+9x^2-4x^3-16x^2-36x+7x^2+28x+63\)
\(=x^2\left(x^2+4x+9\right)-4x\left(x^2+4x+9\right)+7\left(x^2+4x+9\right)\)
\(=\left(x^2+4x+9\right)\left(x^2-4x+7\right)\)
c) \(\left(x^2+2x+7\right)+\left(x^2-2x+4\right)\left(x^2+2x+3\right)\left(1\right)\)
Ta có : \(x^3-8=\left(x-2\right)\left(x^2+2x+4\right)\)
\(\Rightarrow x^2+2x+4=\dfrac{x^3-8}{x-2}\)
\(\left(1\right)\Rightarrow\left[\left(\dfrac{x^3-8}{x-2}+3\right)\right]+\left(x^2-2x+4\right)\left[\left(\dfrac{x^3-8}{x-2}-1\right)\right]\)
\(=\left[\left(\dfrac{x^3-3x-14}{x-2}\right)\right]+\left(x^2-2x+4\right)\left[\left(\dfrac{x^3-2x-5}{x-2}\right)\right]\)
\(=\dfrac{1}{x-2}\left[x^3-3x-14+\left(x^2-2x+4\right)\left(x^3-2x-5\right)\right]\)
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= \(x^4-2x^3-6x^3+12x^2-x^2+2x+6x-12\)
= \(x^3\left(x-2\right)-6x^2\left(x-2\right)-x\left(x-2\right)+6\left(x-2\right)\)
= \(\left(x-2\right)\left(x^3-6x^2-x+6\right)\)
= \(\left(x-2\right)\left(x^2\left(x-6\right)-\left(x-6\right)\right)\)
= \(\left(x-2\right)\left(x-6\right)\left(x-1\right)\left(x+1\right)\)
x4 - 8x3 + 11x2 + 8x - 12
= (x3 - 7x2 + 4x + 12)(x - 1)
= (x3 - 8x + 12)(x + 1)(x - 1)
= (x - 6)(x - 2)(x + 1)(x - 1)
![](https://rs.olm.vn/images/avt/0.png?1311)
x4 + 4
= (x2)2 + 22
= x4 + 2.x2.2 + 4 – 4x2
(Thêm bớt 2.x2.2 để có HĐT (1))
= (x2 + 2)2 – (2x)2
(Xuất hiện HĐT (3))
= (x2 + 2 – 2x)(x2 + 2 + 2x)
![](https://rs.olm.vn/images/avt/0.png?1311)
Sửa đề: x^4+4y^4
=x^4+4x^2y^2+4y^4-4x^2y^2
=(x^2+2y^2)^2-4x^2y^2
=(x^2-2xy+2y^2)(x^2+2xy+2y^2)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Áp dụng HĐT 5 thu được ( 2 a - 3 b ) 3 .
b) Ta có 8 x 3 + 12 x 2 y + 6 xy 2 + y 3 = ( 2 x + y ) 3 .
Áp dụng HĐT 7 với A = 2x + y; B = z
( 2 x + y ) 3 - z 3 = (2x + y - z)(4 x 2 + y 2 + z 2 + 4xy + 2xz + zy).
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^2-8x+12=\left(x^2-6x\right)-\left(2x-12\right)=x\left(x-6\right)-2\left(x-6\right)=\left(x-2\right)\left(x-6\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(\left(x-6\right)\left(x-2\right)\left(x-1\right)\left(x+1\right)\)
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