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b: 6x^2-24y^2
=6(x^2-4y^2)
=6(x-2y)(x+2y)
c: =(4x)^3-(3y)^3
=(4x-3y)(16x^2+12xy+9y^2)
d: x^4-2x^3-x^2
=x^2(x^2-2x-1)
![](https://rs.olm.vn/images/avt/0.png?1311)
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Lời giải:
a.
$64x^2-24y^2=8(8x^2-3y^2)=8(\sqrt{8}x-\sqrt{3}y)(\sqrt{8}x+\sqrt{3}y)$
b.
$64x^3-27y^3=(4x)^3-(3y)^3=(4x-3y)(16x^2+12xy+9y^2)$
c.
$x^4-2x^3+x^2=(x^2-x)^2=[x(x-1)]^2=x^2(x-1)^2$
d.
$(x-y)^3+8y^3=(x-y)^3+(2y)^3=(x-y+2y)[(x-y)^2-2y(x-y)+(2y)^2]$
$=(x+y)(x^2-4xy+7y^2)$
a) \(64x^2-24y^2\)
\(=8\left(8x^2-3y^2\right)\)
b) \(64x^3-27y^3\)
\(=\left(4x\right)^3-\left(3y\right)^3\)
\(=\left(4x-3y\right)\left(16x^2+12xy+9y^2\right)\)
c) \(x^4-2x^3+x^2\)
\(=x^2\left(x^2-2x+1\right)\)
\(=x^2\left(x-1\right)^2\)
d) \(\left(x-y\right)^3+8y^3\)
\(=\left(x-y+2y\right)\left(x^2-2xy+y^2-2xy+2y^2+4y^2\right)\)
\(=\left(x+y\right)\left(x^2-4xy+7y^2\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1 :
\(x^2-6x+8=x^2-2x-4x+8=x\left(x-2\right)-4\left(x-2\right)=\left(x-4\right)\left(x-2\right)\)
Bài 2 :
\(x^8+x^7+1=x^8+x^7+x^6+x^5+x^4+x^3+x^2+x+1-x^6-x^5-x^4-x^3-x^2-x\)
\(=x^6\left(x^2+x+1\right)+x^3\left(x^2+x+1\right)+x^2+x+1-x^4\left(x^2+x+1\right)-x\left(x^2+x+1\right)\)
=\(\left(x^2+x+1\right)\left(x^6+x^3+1-x^4-x\right)\)
Tick đúng nha
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\(=6x\left(-y^2+x^2+2x+1\right)\\ =6x\left[\left(x^2+2x+1\right)-y^2\right]\\ =6x\left[\left(x+1\right)^2-y^2\right]\\ =6x\left(x+1-y\right)\left(x+1+y\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(6x^2+7x+2\\ =6x^2+3x+4x+2\\ =3x\left(2x+1\right)+2\left(2x+1\right)\\ =\left(3x+2\right)\left(2x+1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
đặt y=x2+1
=>y2=(x2+1)2
y2=x4+2x2+1
đặt P(x)=x^4+6x^3+11x^2+6x+1
=x4+2x2+1+6x3+6x+9x2
=x4+2x+1+6x(x2+1)+9x2
thay y2=x4+2x2+1 và y=x2+1 ta được
Q(y)=y2+6xy+9x2
=(y+3x)2
thay y=x2+1 ta được:
(x2+3x+1)2
vậy x^4+6x^3+11x^2+6x+1=(x2+3x+1)2
=6(x^2-4y^2)
=6(x-2y)(x+2y)
\(6x^2-24y^2=6\left(x^2-4y^2\right)\)
\(=6\left(x-2y\right)\left(x+2y\right)\)