Phân tích đa thức thành nhân tử:
a) 27x6 - 8x3
b) x6 - y6
c) y9 - 9x2y6 + 27x4y3 - 27x6
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a) x2+x-2
= x2-x+2x-2
= x(x-1)+2(x-1)
= (x+2)(x-1)
b) 2x2+5x+3
= 2x2+2x+3x+3
= 2x(x+1)+3(x+1)
= (2x+3)(x+1)
c) 3x2+5x-2
= 3x2+6x-1x-2
= 3x(x+2)-1(x+2)
= (3x-1)(x+2)
\(=\left(x^6+2x^5+x^4\right)-2\left(x^5+2x^4+x^3\right)+2\left(x^4+2x^3+x^2\right)\)
\(=x^2\left(x^2+x\right)^2-2x\left(x^2+x\right)^2+2\left(x^2+x\right)^2\)
\(=\left(x^2+x\right)^2\left(x^2-2x+2\right)\)
\(=x^2\left(x+1\right)^2\left(x^2-2x+2\right)\)
\(x-y=\left(\sqrt{x}-\sqrt{y}\right)\left(\sqrt{x}+\sqrt{y}\right)\)
a: \(x^4+3x^3+x^2+3x\)
\(=x\left(x^3+3x^2+x+3\right)\)
\(=x\left(x+3\right)\left(x^2+1\right)\)
c: \(x^2-xy-x+y\)
\(=x\left(x-y\right)-\left(x-y\right)\)
\(=\left(x-y\right)\left(x-1\right)\)
\(2x^2+x-6\)
\(=2x^2-3x+4x-6\)
\(=x\left(2x-3\right)+2\left(2x-3\right)\)
\(=\left(2x-3\right)\left(x+2\right)\)
\(6x^2-13x+6\)
\(=6x^2-9x-4x+6\)
\(=\left(2x-3\right)\left(3x-2\right)\)
\(3x^2-14x-5=3x\left(x-5\right)+\left(x-5\right)=\left(x-5\right)\left(3x+1\right)\)
\(27x^6-8x^3=x^3\left(27x^3-8\right)=x^3\left[\left(3x\right)^3-2^3\right]=x^3\left(3x-2\right)\left(9x^2+6x+4\right)\)
\(x^6-y^6=\left(x^2\right)^3-\left(y^2\right)^3=\left(x^2-y^2\right)\left(x^4+x^2y^2+y^4\right)\)
\(=\left(x-y\right)\left(x+y\right)\left[\left(x^2+y^2\right)^2-x^2y^2\right]\)
\(=\left(x-y\right)\left(x+y\right)\left(x^2+y^2+xy\right)\left(x^2+y^2-xy\right)\)
\(y^9-9x^2y^6+27x^4y^3-27x^6=\left(y^3\right)^3-3.\left(y^3\right)^2.\left(3x^2\right)+3.y^3.\left(3x^2\right)^2-\left(3x^2\right)^3\)
\(=\left(y^3-3x^2\right)^3\)