Phân tích đa thức thành nhân tử
d) 27x^3-1/64
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27x3 + 108x2 + 114x + 64 = ( 3x )3 + 3.( 3x )2.4 + 3.3x.42 + 43 = ( 3x + 4 )3
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(27x^3+27x^2+9x+1=\left(3x+1\right)^3\)
b) \(-x^3-3x^2-3x-1=-\left(x^3+3x^2+3x+1\right)=-\left(x+1\right)^3\)
c) \(-8+12x-6x^2+x^3=\left(x-2\right)^3\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(27x^3-27x^2+18x-4=27x^3-9x^2-18x^2+6x+12x-4\)
\(=9x^2\left(3x-1\right)-6x\left(3x-1\right)+4\left(3x-1\right)\)
\(=\left(3x-1\right)\left(9x^2-6x+4\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^3+3x^2+3x+1-27x^3=-26x^3+3x^2+3x+1\)
\(=-26x^3+13x^2-10x^2+5x-2x+1\)
\(=\left(2x-1\right).\left(-13x^2-5x-1\right)\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x^3+27x+\left(x+3\right)\left(x-9\right)\)
⇒\(x^3+27x+x^2-6x-27\)
⇒\(x^3+x^2+21x-27\)
Chịu
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\(64-27x^3=4^3-\left(3x\right)^3=\left(4-3x\right)\left(16+12x+9x^2\right)\)
\(27x^3-\dfrac{1}{64}\)
\(=\left(3x\right)^3-\left(\dfrac{1}{4}\right)^3\)
\(=\left(3x-\dfrac{1}{4}\right)\left(9x^2+\dfrac{3x}{4}+\dfrac{1}{16}\right)\)